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Connecticut Agricultural College 

Vol 2.4:5 3^ 

Class No. ff y 



Date Ijal . 1 'L 

19 1 


BOOK 570.H917 c. 1 


3 T1S3 001373bM fl 


This Book may be kept out 


only and is subject to a fine of 
TWO GENTS a day thereafter. 
It will be due on the day indicated 

JAN 3 191^ 

Digitized by the Internet Archive 
in 2013 

Farmhouse and favorable environment in the coiintrv, 

Favorable city environment : two-family houses in a residential section of 

large city. 



Presented in Problems 











Copyright, 1914, by 

Copyright, 1926, by 





DuKiNG the past few years, the views of educators on the place 
of biological science in the secondary school have become more 
definite. The report of the Committee of the National Education 
Association on the ^'Reorganization of Science in Secondary 
Schools " is beginning to make its impress on the minds of thinking 
teachers of science. The junior high school movement, with the 
accompanying improvement in the teaching of elementary science, 
is giving a background of science phenomena that the children of 
a decade ago did not have. Health teaching and environmental 
science teaching have produced certain fundamental science con- 
cepts on which a course in biological science may be built. 

While the place of biological science is not fixed in all parts of 
this country, the tendency is well marked to place it in the tenth 
year of the school curriculum.^ Recognizing this, New Civic 
Biology has attempted to build on the unorganized science facts 
that the high school pupil has already assimilated. The trend 
toward better health and citizenship building has been recognized, 
and it is hoped that this book will work toward the ideal develop- 
ment of efficient, thinking citizens. 

A course in biology in the secondary school must be determined 
by other factors than the mere training of the teacher. It must 
reach the capabilities of the student, it must appeal to his interest ; 
it must interpret his environment. And most important of all, 
it must, by means of the vehicle of the problem and the project, 
train him in the technique of thinking. Ideas, not types, should 
be the ultimate development of the laboratory work. As Dr. 
Walter so well points out, the environmental conditions are often 
more important than the type. Most important, too, are the 

^ See " The Place of Science in the Secondary School," G. W. Hunter, School Review, 
May-June, 1925. 



applications of modern biology in the daily life of the student, for 
it is this sort of work that has the greatest appeal. 

The chief difficulty is not so much in knowing what to teach as 
in knowing what not to teach. The topics included in this book 
are those considered most vital in a well-rounded course in ele- 
mentary biology directed toward civic betterment. The physio- 
logical functions of plants and animals, the hygiene of the indi' 
vidual within the community, conservation and the betterment of 
plant and animal products, the big underlying biological concepts 
on which societ}^ is built, have all been used to the end that 
the pupil rudij become a better, stronger, and more unselfish citizen. 

At the beginning of each of the following chapters (except the 
first and the last) are a series of suggested problems. These 
should serve as a review of the chapter for both teacher and stu- 
dent. They constitute, to a degree, the ke}^ which opens the way 
to the understanding of the chapter. Following the problems 
are laboratory suggestions, many of which are worked out fully 
in Hunter's Laboratory Problems in Civic Biology. 

At the end of each chapter is a list of books which have proved 
their usefulness either as problem and project references for stu- 
dents or as aids to the teacher. Most of the books mentioned are 
within the means of the small school. 

For a general introduction to physiological biology, Sedgwick 
and Wilson, General Biology, Henr}^ Holt and Company ; Needliam, 
General Biology, Comstock Publishing Company ; and Shull, Prin- 
ciples of Animal Biology, The IMcGraw Hill Company, are most 
useful and inspiring books. 

One book stands out from the pedagogical standpoint as most 
helpful. It is Twiss, Principles of Science Teaching, The Mac- 
millan Company. Other books of value from the teacher's stand- 
point are Curtis, Investigations in the Teaching of Science, P. 
Blakiston's Son and Compam^ ; Frank, " How to Teach General 
Science, P. Blakiston's Son and Company ; Hodge, Nature Study 
and Life, Ginn and Company ; Downing, Teaching Science in the 
Schools, University of Chicago Press ; Brownell and Wade, The 
Teaching of Science, The Century Company ; Ganong, The Teach- 
ing Botanist, The Macmillan Company; and Eikenberry, The 
Teaching of General Science, University of Chicago Press. 


Every biology teacher should also have access to the Science 
News Letter, published by Science Service, School Science and 
Mathematics, Turton and Warner, Chicago, and the General 
Science Quarterly, W. G. Whitman, Salem, Mass., as all these pub- 
lications contain much of value to the secondary school teacher of 

The sincere thanks of the author are extended to all who by 
advice and suggestions have helped make this book possible. 
The following have read the manuscript in its entirety : Annah P. 
Hazen, Head of the Department of Biology in the Eastern Dis- 
trict High School, City of New York ; Leshe L. Hunt, Department 
of Biology, Galesburg High School, Galesburg, 111. ; George W. 
Hunter, III, Assistant in Biology, University of Illinois, Urbana, 
111. ; Rosemary F. Mullen, Head of the Department of Biology, 
Washington Irving High School, City of New York; Mary E. 
Robb, Department of Biology, Hyde Park High School, Chicago, 
111. ; Jesse M. Shaver, Department of Biology, Peabody College, 
Nashville, Tenn. ; Professor A. C. Walton, Department of Biology, 
Knox College; and Dr. Frank M. Wheat, Head of the Depart- 
ment of Biology, George Washington High School, City of New 
York. Dr. Henry B. Ward, Head of the Department of Zoology 
of the University of Illinois, and Mr. Robert Sterling Yard, 
Executive Secretary of the National Parks Association, have also 
offered valuable suggestions on certain parts of the book. 

Thanks are due, also, to Professor E. B. Wilson, Mr. William 
C. Barbour, Dr. John A. Sampson, W. C. Stevens, and Wilham 
Beebe; to the United States Department of Agriculture; the 
New York Aquarium; the Charity Organization Society; and 
especially to the American Museum of Natural History, for per- 
mission to copy and use certain photographs and cuts which have 
been found useful in teaching. Dr. Frank M. Wheat made most 
of the line drawings prepared for this book and has given many 
valua,ble suggestions. 



I. The General Problem — Some Reasons for the Study 

OF Biology ......... 1 


11. The Environment of Plants and Animals ... 7 
HI. Living Things and the Environment .... 13 
IV. The Interrelations of Plants and Animals . . 24 


V. The Building Material of Living Things ... 43 

VI. Plant Growth and Nutrition. Causes of Growth . 51 
VII. Organs of Nutrition. Roots in Relation to the 

Soil 63 

VIII. How Green Plants Make Food 75 

IX. The Circulation and Final Uses of Food by Plants 87 



X. The Simplest Organisms 95 

XI. The Relations of Plants to Animals .... 102 


XII. Animal Organisms. The Human Machine . . . 107 

XIII. A Study of Foods and Dietaries 118 

XIV. Dangers from Food Adulteration, Alcohol, and 

Drugs 138 

XV. How Food is Prepared for Body Uses . . . 146 

XVI. The Blood and its Circulation 162 

XVII. Respiration and Excretion 177 




XVIII. How Body Control is Brought About. . . . 192 
XIX. How Habits are Formed 208 


XX. Reproduction in Plants and Animals . . . .219 
XXL Classification of Plants and Animals .... 234 


XXII. Bacteria and Disease 253 

XXIII. How We Fight Bacterial Diseases .... 268 

XXIV. The Relations of Animals to Disease .... 278 
XXV. Man's Improvement of his Environment . . . 292 


XXVI. Our Forests, their Uses and Need of Protection . 313 
XXVII. The Value of Green Plants to Man . . . .323 
XXVIII. Plants without Chlorophyll in their Relation to 

Man 334 

XXIX. The Economic Importance of Animals .... 347 
XXX. Conservation and its Lessons 368 


XXXI. Plant and Animal Breeding 380 

XXXII. The Improvement of the Human Race . . . 394 
XXXIII. Some Great Names in Biology 405 

Glossary . . . • 415 

Weights, Measures, Laboratory Equipment . . 429 
Index 431 




The Study of Biology. — The word hioVogy comes from two Greek 
words, hios (Hfe) and logos (word or study). Biology, then, is the 
study of things that are aHve, both plants and animals. And 
since man is the highest and most important of all living creatures, 
it is only fitting that emphasis should be placed chiefly on the 
science underlying man's health and well-being. 

Biology is a modern science ; it has found its way into most 
high schools, and an. increasingly large number of girls and boys 
are engaged in its study every year. These questions might well 
be asked by any of the students : Why do I take up the study of 
biology? Of what practical value is it to me? Besides the dis- 
cipline it gives me, is there anything that I can take away which 
will help me in my future life ? 

Knowing about Nature is Worth While. — Most of us know 
something about biology. We are constantly meeting or playing 
with or collecting living things. We visit the '^ zoo," we have 
pets, or gardens, we read the papers and magazines ; thus we have 
some knowledge. But this knowledge is often not very accurate.^ 
It is worth while from the standpoint of pleasure in one's life to^ 
know a little about the varied forms of life that one may meet on 
a walk in the fields or a stroll along the ocean beach. Even for 
the pleasure it gives us, we should study biology. 

Physiology and Hygiene. — If the study of biology will give us a 
better understanding of our own bodies and their care, then it cer- 
tainly is of use to us. That phase of biology known as physioVogy 
deals with the uses of the parts of a plant or an animal ; human 
physiology and hygiene (hi'ji-en) deal with the uses and care of 
the parts of the human body. The prevention of sickness is due 
in a large part to the study of hygiene. It is estimated that over 



twenty-five per cent of the deaths that occur yearly in this country 
could be averted if all people lived in a hygienic manner. In its 
application to the life of each of us, as a member of a family, 

as a student in school, and 
as a future citizen, a knowl- 
edge of hygiene is of the 
greatest importance. 

The Uses of Plants to 
Man. — But there are other 
reasons why an educated 
person should know some- 
thing about biology. We 
do not always realize that 
if it were not for the green 
plants, there would be no 
animals on the earth. 
There is a wonderful bal- 
ance of life on the earth, 
maintained by the energy 
of the sun. We shall see 
later that green plants, like 
factories, turn raw mate- 
rials into food products and 
thus furnish food to ani- 
mals. Even the meat-eat- 
ing animals feed upon those 
that feed upon plants. 
Plants furnish man with 
the greater part of his food 
in the form of grains and 
cereals, fruits and nuts, 
edible roots and leaves; 
they provide his domesti- 
cated animals with food ; 
they give him timber for his houses and wood and coal for his fires ; 
they pro\dde him with pulp wood, from which he makes his paper, 
and oak galls, from which he can make ink. Some of man's 
clothing and the thread with which it is sewed together come from 

Blossoms and bolls of the cotton plant. 
More cloth is made of cotton than of any 
other fiber. 


fiber-producing plants. Most medicines, beverages, flavoring ex- 
tracts, and spices are plant products, while plants are used in hun- 
dreds of ways in the arts and trades, yielding varnishes, dyestuffs, 
rubber, and other products. 

Bacteria in their Relation to Man. — In still another way, cer- 
tain plants vitally affect mankind. Tiny plants, called bacteria, 
so small that millions can exist in a single drop of fluid, exist 
almost everywhere about us, — in water, soil, food, and air. 
They play a tremendous part in shaping the destiny of man on 
the earth. They help him in that they act as scavengers, causing 
things to decay ; thus they remove the dead bodies of plants and 
animals from the surface of the earth, and turn tliis material back 
to the ground ; they assist the tanner ; they help make cheese and 
butter ; they improve the soil for crop growing, so the farmer can- 
not do without them. But likewise they sometimes spoil our meat 
and fish, our vegetables and fruits ; they also sour our milk, and 
may make our canned goods spoil. Worst of all, they cause many 
diseases, such as typhoid, tuberculosis, pneumonia, and colds. 
It is estimated that half the deaths that occur each year are caused 
by these plants. So important are the bacteria that a subdivision 
of biology, called hacterioV ogy , has been named for them, and 
hundreds of scientists are devoting their lives to the study of bac- 
teria and their control. The greatest of all bacteriologists, Louis 
Pasteur (pas-ttir')/ once said, ''It is within the power of man to 
cause all parasitic diseases [most of which are caused by bacteria] 
to disappear from the world." His prophecy is gradually being 
fulfilled. Each year sees some disease such as diphtheria, typhoid, 
or scarlet fever conquered or brought under better control through 
scientific knowledge, and it may be the lot of some boys or girls 
who read this book to do their share in such work. 

The Harm done by Some Animals. — Animals also play an im- 
portant part in the world in causing and in carrjdng diseases. Ani- 
mals that cause disease are usually tiny and live in other animals 
as parasites; that is, they get their living from the hosts on which 
they feed and in so doing may cause disease or the death of the 
hosts. Among the diseases caused by parasitic animals are ma- 
laria, yellow fever, sleeping sickness, and the hookworm disease. 

1 The diacritic marks are those used in the Webster school dictionaries. 


Animals also carry disease germs ; flies, mosquitoes, rats, and cats 
are well known as spreaders of diseases. 

From a monetary standpoint, insects do much harm. It is esti- 
mated that in this country alone in 1924 they were responsible for 
considerably over $2,000,000,000 worth of damage by eating crops, 
stored food, and other things. 

The Uses of Animals to Man. — We all know the uses man 
has made of the domesticated animals for food and as beasts of 

Cows in a model stable, with milking machines in operation. There are 
many state laws and city ordinances for the regulation of dairies and the sale 
and distribution of milk. 

burden. But many other uses are found for animal products, 
and materials made from animals. Wool, furs, leather, hides, 
feathers, and silk are examples. The arts make use of ivory, tor- 
toise shell, corals, and mother-of-pearl ; from animals come per- 
fumes and oils, glue, and various other commodities. 

Relations of Plants and Animals. — Most plants and animals 
stand in a relation of mutual helpfulness, plants providing food 
and shelter for animals, and animals giving off waste materials 
useful to plants in the making of food. We also learn that plants 
and animals need the same conditions in their surroundings in 
order to live : water, air, food, a favorable temperature, and usually 


light. The Hfe processes of both plants and animals are essentially 
the same, and the living matter in a tree is as much alive as is the 
living matter in a fish, a dog, or a man. 

Plants and animals are living things, taking what they can from 
their surroundings ; they enter into competition with one another, 
and those which are best fitted for life outstrip the others. Each 
kind of animal and plant tends to vary from its nearest relatives 
in all details of structure. The strong may hand down to their 
offspring characteristics which make them winners. Health and 
strength of body and mind are factors which tell in winning. 

Man has made use of this message of nature, and has dei^eloped 
improved breeds of horses, cattle, and other domestic animals. 
Plant breeders, likewise, have selected plants or seeds that have 
shown a tendency to improve, and thus have raised liardier and 
more fruitful domesticated plants. Man's dominion over the liv- 
ing things of the earth is tremendous. This is due to his under- 
standing of the principles which underlie the science of biology. 

Photo from Neiv York State Conservation Commission 

How does the forest help the stream ? 

The Importance of Forests. — Still another reason why we should 
study biolog;)^ is that we may work intelligently for the conserva- 
tion of our natural resources, especially of our forests. The living 
forest is valued for its beauty and its health-giving properties, 


and because it holds water in the earth. It keeps the water from 
drying out of the soil quickly on hot days and from running off 
quickly on rainy days. Thus a more even supply of water is given 
to our rivers, and freshets are prevented. Regions that have 
been deforested, such as parts of China, Italy, and France, are novv 
subject to floods and are barren in many places. On the forests 
depend our supply of timber, much of our water power, and the 
commercial importance of navigable rivers. 

Biology in Relation to Society. — The study of biology also ought 
to make us better men and women by teaching us that unselfish- 
ness exists in the natural world as well as among the highest 
members of society. Animals, lowly and complex, sacrifice their 
comfort and their very lives for their young. In insect colonies 
the welfare of the individual is given up for the best interests 
of the community. The law of mutual give and take, of sacrifice 
for the common good, is seen everywhere. This should teach us, 
as we come to take our places in society, to be willing to give up 
our individual pleasure or selfish gain for the good of the com- 
munity in which we live. Thus the application of biological prin- 
ciples will benefit society. 

Biology in Relation to Citizenship. — Finally, proper qualifica- 
tions for citizenship are the biggest return we uisij expect from 
our high school career. How can a man or woman become an 
intelligent voter without at least some understanding of biology? 
Think of the number of times the average voter is asked to ex- 
ercise judgment on matters concerning the health and wealth of 
the community. How can he do this without some knowledge of 
the facts ? And how can he exercise judgment if he has no previous 
training? Science, especially through experiments, helps us to 
make intelligent judgments. Through the projects and experi- 
ments you carry out, your ability to think straight as a citizen 
will be aided. And when we realize that in the last half century 
the application of biology to health has lengthened the average 
span of life ten years ; when we see that applications of biology in 
industry have made the life of the average workman far safer than 
before, we understand the need of real knowledge of applied biol- 
ogy. It is the purpose of this book to help the boys and girls of 
to-day to become healthy, intelligent, thinking voters of to-morrow 




Problems : ^ To discover some of the factors of the environment 
of plants and animals. 

To discover the chemical nature of the environment, and of plants 
and animals. 

Laboratory Suggestions ^ 

Demonstration. The composition of the air. 
Demonstration. The separation of water into its elements. 
Laboratory experiment. To determine the solubility of different sub- 

Demonstration. Oxidation of carbon and the test for carbon dioxide. 

Environment. — Each one of us, no matter where he lives, comes 
in contact with certain surroundings. Air is everywhere around 
us. Light and heat are necessary to us, so much so that we use 
artificial hght at night and artificial heat in winter. Out of doors 
we walk on the soil of a farm or a village, or on a city street, with 
its dirty and hard paving stones. Water and food are a necessary 
part of our surroundings. All these factors — air, light, heat, soil, 
water, food, and other things — together make up our environment. 

But we must not think of the environment as simply the room 
in which we sit, or the town in which we live. Sunlight, on which 
our very existence depends, comes from the center of our solar 
system, 93,000,000 miles away. The water which we use in our 
kitchens may have been piped scores of miles to us : witness the 
water supplies of Los Angeles and of New York. The food we use 

^ The Problems stated at the beginning of each chapter constitute, in a way, a key 
to the text of the chapter. The Laboratory Suggestions are to be used at the dis- 
cretion of the teacher. 



may have come from the deeps of the sea or the far-away tropics. 
Our environment, in a certain sense, includes anything that may 
affect us in that place where we happen to be; this, of course, 
includes all other living things, plant or animal, that may come in 
contact with us during our lives in a given locality. 

All animals, and all plants as well, are surrounded by and use 
the factors of their environment. In order to live, the potted plant 
in the window, the goldfish in the aquarium, your pet dog at 
home, all need air, water, light, a certain amount of heat, and food. 
The Physicist's and Chemist's View of the Environment. — 
Most of us have had some introduction to science and know that 

water, air, soil and rocks, the 
bodies of living things, in short, 
anything that occupies space, is 
called by the physicist matter. 
The chemist in his turn resolves 
all matter into ninety-odd sim- 
ple substances called chemical 
elements. We know that air 
surrounds us, that it has a pres- 
sure of 15 pounds to the square 
inch at sea level, and that, as 
we go up from the earth's sur- 
face, there is less and less air, 
until it ultimately disappears at 
a height of about 200 miles from 
the earth's surface. We know also that the air is composed 
chiefly of two elements, oxygen (ok'si-jen) and nitrogen (ni'tr6-jen), 
there being about one part of oxygen to four of nitrogen. Air 
is a mixture of these gases, together with water vapor, carbon 
dioxide (a chemical compound), and other gases in very small 

Again, by means of the apparatus shown on page 9, the chem- 
ist and physicist, working together, have proved that water is a 
combination of the chemical elements oxygen and hydrogen (hi'dr6- 
jen). In this case, however, the elements are bound together so 
closely that they form a substance called water. This substance, 
which is always composed of a definite proportion of two parts of 

Experiment to show the amount of oxy- 
gen in the air. A before, and B after the 
phosphorus p is lighted. The white fumes 
formed by the combination of oxygen 
with the burning phosphorus settle and 
are dissolved in the water. How high 
does the water rise in the jar? Why? 



hydrogen to one part of oxygen, is expressed by the formula H2O 
by the chemist and is called a chemical compound. 

Both oxygen and hydrogen are colorless, tasteless, and odorless, 
but hydrogen differs from oxygen by igniting with a slight explosion 
when it is mixed with a little air and a burning match or splinter 
is introduced in it. As it burns, drops of water are formed, show- 
ing that the hydrogen is uniting again with oxygen to form water. 
Hydrogen has a great chemical affinity for other elements ; hence 
it is usually found in nature 
combined with other ele- 
ments, as, for example, with 
oxygen in water. 

The Place of Water in the 
Environment. — Water, in 
the form of rain, snow, or 
ice, or in river, lake, or sea, 
forms a very important part 
of our environment. It car- 
ries soil or mineral sub- 
stances, sometimes as sedi- 
ment, sometimes in solution. 
The water of the ocean holds 
salts in solution. If sea water is boiled until it is all evaporated, 
the salts will remain. If water is poured over them, they will 
dissolve or become solutes (s6-lutsO . In other words, the salts 
become divided into very minute particles which distribute them- 
selves through the liquid. But there are great differences in the 
solubility of substances. Some, like common salt or sugar, are 
very soluble ; others, such as lime and iron, very insoluble. Pure 
water containing no solutes is rarely found in nature. 

Oxidation. — Oxygen has the very important property of unit- 
ing with many other substances. The chemical union of oxygen 
with another substance is called oxida'tion. Rapid oxidation pro- 
duces a flame or light. Oxidation, either rapid or slow, may take 
place wherever there is uncombined oxygen. This fact has great 
significance in the understanding of important problems of biol- 
ogy. An example of slow oxidation is seen in the rusting of an 
iron nail. If the rust and nail are weighed, the total weight 

Apparatus for separating water into hydro- 
gen H and oxygen O: c, copper wire, p, plati- 
num wire soldered to the copper, with insula- 
tion so that no copper is exposed in this tube. 
A few drops of sulphuric acid should be added 
to the water, to facilitate the action of the 
electric current. 


will be more than that of the original nail. Do you see why? 
Rust is iron oxide and is formed by the union of iron and oxygen. 
The slow oxidation of many chemical compounds is constantly 
taking place in nature and is a part of the process of decay and of 
brealdng down of complex materials into simpler forms. 

The Composition of the. Soil. — The covering of the earth is 
composed of a mantle of soil and rock. The rock, by the work 
of wind, frost, heat, water, plants, and animals, gradually breaks 
down into small bits to form the soil mantle. This is inorganic 
soil, which is formed usually of several of the elements found in 
rocks, such as cal'cium, so'dium, magne'sium, siVicon, yotas'sium, 
and iron, all combined with oxygen. 

A visit to the woods or to a well-kept garden shows us that there 
is another kind of soil than the inorganic soil just mentioned. This 

is the rich, dark soil containing 
hu'mus. Humus is made up 
largely of dead organic matter, 
the decayed remains of plants and 
animals. If we could test the 
chemical elements to be found in 
humus, we should find nitrogen, 
hydrogen, oxygen, and also car- 
bon, an important element found 
in all organic matter. 

Carbon. — Carbon is found in 
many conditions in nature. It 
is found in the bodies of plants 
and animals, and in coal (fossil 
plants), and it exists in a nearly pure state in the diamond. The 
presence of carbon can usually be detected by partly burning or 
charring a substance ; if carbon is present, some of it remains as 
a black substance without taste or odor. Carbon may be col- 
lected by allowing a candle flame to burn in contact with the under 
side of a sheet of glass. The black deposit is almost pure carbon. 
The Result of the Oxidation of Carbon. — We have seen that a 
candle contains carbon. We can also easily show that part of 
this carbon unites with the oxygen of the air when a candle burns. 
If a candle is burned in a closed jar it soon goes out. If we now 

Percentages of chemical elements in the 
human body. 








test the gas in the closed jar by shaking it with Hme water, a color- 
less liquid/ we find that a milky white precipitate is formed. 
This indicates the presence of a 
gas called carbon dioxide (CO2), 
which is formed by the union 
of one part of carbon with two 
of oxygen of the air. If lime- 
water is shaken in a jar of fresh 
air little or no precipitate will 
be formed. Most of the car- 
bon dioxide, therefore, must 
have come from the burning 

The Composition of Plants ^ 

and Animals. — The soil and /yf /?» 





other things in nature are 
largely composed of chemical 
compounds, a few like water, 
iron rust, and table salt being 
simple, but the greater number 
being very complex. Rocks, 
humus, organic food sub- 
stances, and the bodies of plants 
and animals are all composed 
of chemical compounds. Pro- 
fessor H. F. Osborne of Colum- 
bia University has pointed out 
that the chemical substances 
found in sea water agree very 
closely with those in the human ^J;^^ 
blood. There are other facts Rfomjnfi. 
also which prove that the same 

















Percentages of chemical substances in sea 
chemical elements found in the water and in blood serum. (After Osborn.) 

environment somehow or other 

become organized into the tremendously complex stuff of which 

we find living plants and animals composed. These elements 

^Limewater can be made by shaking a piece of quicklime the size of your fist in 
about two quarts of water. Filter the limewater and keep it in bottles well corked. 


are principally carbon, hydrogen, oxygen, and nitrogen with ten or 
more others in very minute proportions. It is logical to believe 
that living things use the chemical elements in their surroundings 
and in some wonderful manner build up their own bodies from 
the materials found in their environment. How this is done we 
shall learn in later chapters. 

Summary. — This chapter has been in the nature of a review of 
your elementary science ; but it should give you a slightly differ- 
ent view of the environment because it is considered from the 
standpoint of living things. We have seen that the chemist's 
elements and compounds, which give us the factors of the environ- 
ment, air, water, soil, and food, become a part of living things, 
which, when they die, are decomposed to form a part of the soil. 
How this is and why, future chapters will explain. 

Problem Questions 

1 . What are the factors of thb environment ? Why are they so called ? 

2. Are there any factors in the environment which are unnecessary to ani- 
mals ? To plants ? 

3. How are compounds formed? How broken up? 

4. Compare rapid and slow oxidation in all respects. 

5. Name some compounds found in soil. In water. 

6. What is meant by solution ? 

7. What proof have we that living things use the factors of their environ- 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Hunter and Whitman, Civic Science in Home and Community. American 

Book Company. 
Broadhurst, Home and Community Hygiene, Chap. XVI. J. B. Lippincott 

Burkett, Stevens, and Hill, Agriculture for Beginners. Ginn and Company. 
Brigham and McFarlane, Essentials of Geography. • American Book Company. 
Weed, Chemistry in the Home American Book Company. 


Problems : What is " being alive "f 

What are tropismsf 

Of what value are tropisms to a living thing f 

What are adaptations f 

In what respects has man modified his environment? 

Laboratory Suggestions 

Home work. The study of a living plant and a living animal. List functions, 
likenesses, differences. 

Demonstration of some tropisms, plant and animal. 

Field trip. Visit to a museum or botanical garden or zoological park for 
the study of habitat groups. 

A study of some simple adaptations. 

A survey to discover how man has modified his environment. 

A Living Plant and a Living Animal compared. — A walk in the 
fields or a vacant lot on a day in early autumn will give us first- 
hand acquaintance with many common plants which, because of 
their ability to grow under somewhat unfavorable conditions, are 
called weeds. Such plants as the dandelion, butter and eggs, and 
shepherd's purse, are particularly well fitted by nature to produce 
many of their kind, and also are able to thrive under conditions 
which would not easily support life in other less hardy plants. 
Feeding on these and other plants, are several kinds of animals, 
most of them insects. 

If we attempt to compare, for example, a grasshopper with the 
plant on which it feeds, we at once see several points of likeness 
and of difference. Both plant and insect are made up of parts, 
each of which, as the stem of the plant, or the leg of the insect, 
appears to be distinct, but is a part of the whole living plant or 
animal. These parts, such as the leaves of the plant, or the legs of 
the insect, are used by the plant or the animal for definite purposes, 



For example, as we shall see later, the leaf, because of its structure 
and position on the plant, is fitted to receive and use the sun's 
light, while the legs of the insect will be found to be jointed, often 
provided with claws or hooks for holding to a support, and to be 
capable of movement. Such parts of a living plant or animal, 
each having a separate work to do, are 
called organs. Thus plants and animals 
are spoken of as or'ganisms. 

What is being Alive ? — We are all 
aware, through a study of elementary sci- 
ence, that matter may assume several 
forms. Water, for example, when cooled 
sufficiently, becomes ice, or, if heated to 
the boiling point, becomes vapor. In order 
to be changed it has to be acted upon by 
outside forces. But when a plant or an 
animal grows, or moves, or in some other 
way manifests energy, that manifestation 
comes from within the organism. 

We think of things as alive when they do 
something. Yet water may turn a wheel 
and generate electricity, which has a force 
that is capable of ''doing something. " Such 
a force may set off a blast of dynamite. 
Another example is a flash of lightning, 
which may destroy a tree. 
It is not easy to distinguish exactly what it is to be alive, 
any more than it is easy to tell what electricity is or what radioac- 
tivity is. Electricity is a servant of man, but the greatest expert 
cannot tell what the force actually is. Life is a manifestation of 
forces, like a flame or electricity. Every living thing, as we shall 
see later, is like a steam engine or any other machine, in that it 
is a medium used for the transformation of energy. So we had 
best start by trying to see how living things act in their normal 
environment when outside forces influence them. 

Response to Stimuli an Indication of Life. — One of the world's 
greatest biologists, Jacques Loeb (zhak lob), some years ago at- 
tempted to prove that all living things are more or less auto- 

A weed. Notice 
different parts 



matically controlled by the factors of their environment. He 
assumed that all living matter is sensitive and that it responds or 
reacts to the forces of its environment, in very definite ways. 
These forces we call stim'uli (sing, stimulus) ; the response to such a 
stimulus we call a tro'pism. Loeb and his followers have shown 
quite conclusively that living matter responds very definitely to 
temperature, touch, chemical substances, electricity, and various 
other factors of the environment. Response is e\ddently one indi- 
cation of being alive. It is a means by which plants and animals 
adjust themselves to the favorable or unfavorable factors of their 

Living Things show Activity. — Response to stimuli means 
activity or movement. But movement in living things is brought 
about by changes within the organism, while the movement 
of an engine is brought about by the force of burning coal or ex- 
ploding gasoline. Evidently there is a difference here, although 
it is not easy to explain, in our present state of knowledge. 

Method of Growth in Living Things. — The most outstanding 
difference between the living organism and the non-hving engine 
lies in their methods of growth. An expert mechanic may build 
an engine, but no one has ever made a living thing. Growth takes 
place in a crystal or a limestone stalagmite in a caA^e or in the 
familiar example of the icicle, but it is simply accretion or gradual 
addition of non-living material on the outside. But in a plant or 
animal a mysterious growth takes place through taking into the 
body various substances quite unlike the body material. The 
making over of materials in a living body to form the living stuff 
is called assimilation. 

Reproduction in Living Things. — Another striking attribute 
of living matter is its ability to reproduce its kind. Living plants, 
by seeds, sprouts, buds, or cuttings, form new li\dng plants, and 
we all know that some animals hatch from eggs and others are 
born alive. This act of reproduction is another activity by means 
of which we can tell that an organism is alive. But we can no 
more say what assimilation or growth or reproduction is than we 
can tell what electricity is. They are activities of living things. 

How Plants and Animals react to the Primary Factors of their 
Environment. — Water. It is a weU-known fact that most living 


things need water, in order to sustain life. The roots of green 
plants grow toward a source of water. Some animals appear to 
be stimulated to move toward water, whereas others move away 
from moisture. In the words of science, they show hydrot'ropism, 
and are positively or negatively hydrotrop'ic. Water is of so much 
importance to man that from the time of the Caesars until now" he 
has spent enormous sums of money to bring pure water to his cities. 
The United States government has spent millions of dollars on 
irrigation to bring the water needed to support life in the western 
desert lands. 

Light. Light is another important factor of the environment. 
A study of the leaves on any green plant growing near a window 

will convince one that the 
stems of such plants grow 
toward the light, and that 
the leaves are held in such 
positions that they get a 
maximum amount of sun- 
light. All green plants are 
thus influenced by the sun. 
Other plants which are not 
green seem either indiffer- 
ent or negatively influ- 
enced by the stimulus of light. The direction, as well as the 
intensity of light, is an important factor. Animals may or may 
not be attracted by light. A moth, for example, will fly toward a 
flame ; an earthworm will move away from light. Movements 
toward or away from light are known as positive or negative 
heliot'ropism (Gr. helios, sun) or photofropism. Some animals 
prefer a moderate or weak intensity of light and live in shady 
forests or jungles, prowling about at night. ■ Others seem to need 
strong light. Man himself is most comfortable and works most 
efficiently in a moderate intensity of light. 

Gravity. Another factor influencing both plants and animals 
is gravity. Roots of plants, for example, grow downward and are 
thus said to be positively geotrop^ic. The stem, on the other hand, 
grows upward; it is negatively geotropic. Many animals show this 
response to gravity — geot'ropism — in very definite ways. 

The effect of light upon a growing plant. 


Food or Chemical Substances. We shall see later that plants are 
greatly influenced by the presence or absence of chemical sub- 
stances in the soil. Since such substances are absorbed by the 
plant and later built into the organism, we can easily see that 
responses of this sort are of the utmost importance. As we well 
know, animals, including man, are much influenced by some kinds 
of chemical substances that we call foods, and may be seriously 
affected by other combinations of chemicals called poisons. Re- 
sponse to chemical substances is called chemot'ropism. 

Temperature. Living things are affected by heat or the absence 
of it. Animals and small plants that are able to move in the 
water frequently go from a cooler to a warmer part of the fluid, 
or away from a temperature that becomes unfavorable to their ex- 
istence. They are thus ssiid to show thermotropism. In cold weather 
green plants either die or temporarily suspend their life activities, 
becoming dormant. Likewise, small animals, such as insects, may 
be killed by cold or may hibernate under stones or boards. Their 
life activities are slowed down until the coming of warm weather. 
Bears and some other large animals go to sleep during the winter and 
awake, thin and hungry, on the approach of warm weather. Ani- 
mals and plants used to certain temperatures are killed if removed 
from them. Even man, one of the most adaptable of all animals, 
cannot stand great changes without discomfort and sometimes 
death. He heats his houses in winter and sometimes cools them 
in summer so as to have the amount of heat most acceptable to 
him, i.e., about 70° Fahrenheit. 

The Value of Tropisms. — A study of hundreds of experiments 
with plants and animals shows us that tropisms are of the greatest 
use to them. Response to a favorable stimulus results in placing 
the living plant or animal where it can better succeed in the world. 
And in general, tropisms bring the organism into adjustment with 
its environment. 

The Environment determines the Kinds of Animals and Plants 
within it. — In our study of geography we learned that certain 
luxuriant growths of trees and climbing plants are characteristic 
of the tropics, with their moist, warm climate. The tropical jungle 
is often a tangle of long climbing plants, the leaves festooned over 
the trunks of tall trees, while the jungle floor is covered with a 


lower growth of shade-loving plants. Animal life abounds, al- 
though insects and birds predominate in these tropical regions. 

Photo Galloway 

Dense tropical jungle in the Amazon Valley. 

Most of US live in conditions of temperate climate, with its 
almost complete absence of plant growth in winter but v^ith 
luxuriance of life in summer. No boy or girl can fail to notice 
that temperature must play a very important part in determin- 
ing not only what will grow in a given locality, but also how it 
will grow. 


As we go northward it is still more evident that temperature plays 
an important part in determining the kind and amount of plant 
growth. A glance at the picture will show this. The factors of the 
environment evidently determine the kind of life to be found in a 
given locality. If, for example, temperate forms of life were intro- 
duced by man into the tropics, they would either die or gradually 
change so as to become fitted to live in their new environment. 
English sheep with long wool soon died when removed to Cuba, 












, . ^ ^ X T'. t>y,. 

, //x/^^^<!^ 

x^^ /^'^^^ 


Photo Galloway 

Vegetation in northern Alaska, where no trees grow. The reindeer feed 
on grasses and lichens. 

where the climate is very warm. They were not fitted or adapted 
to live in their changed environment. 

Adaptations. — Not only are plants and animals fitted to live 
under certain conditions, but each part of the body may be fitted 
to do certain work. I notice that as I write these words the fingers 
of my right hand grasp the pen firmly and the hand and arm exe- 
cute some very complicated movements. This they are able to 
do because of the free movement given through the arrangement 
of the delicate bones of the wrist and fingers, their attachment 
to the bones of the arm, a wonderful complex of muscles which 
move the bones, and a directing nervous system which plans the 
work. Because of the peculiar fitnesses in the structure of the 


hand for this work we say it is adapted to its function of grasping 
objects. Each part of a plant or animal is usually suited for some 
particular work. The root of a green plant, for example, is fitted to 
take in water by having tiny absorbing structures growing from it. 
The stems have pipes or tubes to convey liquids up and down and 
are strong enough to support the leafy part of the plant. The 
thin, flat leaves are arranged to receive a very large amount of 

sunlight and to act as 
solar engines. Each part 
of a plant does work, and 
is fitted, by means of cer- 
tain structures, to do that 
work. The lungs of a 
land animal are adapted 
for taking oxygen from 
the air, while the gills of 
a fish can take their sup- 
ply only from water; 
that is, only from the air 
that is dissolved in water. 
It is because of such adap- 
tations that living things 
are able to do their work 
within their particular 

Plants and Animals 
and their Natural En- 
vironment. — Those of us 
who have tried to keep 
potted plants in the 
schoolroom know how difficult it is to keep them healthy. Dust, 
foreign gases in the air, lack of moisture, and other causes make the 
artificial environment in which they are placed unsuitable for them. 
A goldfish placed in a small glass jar with no food and no green water 
plants soon dies. The artificial environment lacks something that 
the fish needs. Each plant and animal is limited to a certain en- 
vironment because of certain individual needs which can be pro- 
vided for only by that particular environment. 

A natural barrier across a stream. No trout would 
be found above this fall. Why not? 



Changes in Environment. — Most plants and animals do not 
change their environment. Trees, green plants of all kinds, and 
some animals remain fixed in one spot practically all their hves. 
Certain tiny plants and most animals move from place to place, 
either in air, in water, on the earth or in the earth, but they main- 
tain relatively the same conditions in environment. A high moun- 
tain chain with intense cold at the upper altitudes would be a barrier 
over which, for example, 
a soft-bodied animal like 
a worm or a snail could 
not travel. Certain 
species of trout are found 
on the western side of the 
continental divide and 
other species on the 
eastern side. Fish will 
migrate up a stream until 
they come to a fall too 
high for them to jump. 
There they must stop be- 
cause their environment 
limits them. 

Man in his Environ- 
ment. — Man, while he 
is like other animals in 
requiring heat, light, 
water, and food, differs 
from them in that he has 
come to live in a more 
or less artificial environ- 
ment. Men who lived on the earth thousands of years ago did 
not wear clothes or have elaborate homes of wood, brick, or 
stone. They did not use fire, nor did they eat cooked foods. In 
short, by slow degrees, civilized man has come to live in an en- 
vironment changed from that of other animals. He has learned 
to build houses and to use fire. The living together of men in 
communities has caused certain needs to develop. Many things 
can be supplied in common, as water, milk, and fuel. Wastes 

H. NSW CIV. BIOL. — 3 

An unfavorable city environment. Compare 
with the favorable city environment shown in 
the frontispiece. 


of all kinds in a town or city have to be disposed of. Houses 
have come to be placed close together, or piled one on top of another, 
as in modern apartment buildings. Fields and trees, in fact most 
aspects of country outdoor life have virtually disappeared in a 
large city. City-dwelling man has come to live in an artificial 

Care and Improvement of One's Environment. — Man can 
modify or change his surroundings by making this artificial envi- 
ronment favorable to live in. He can heat his dwellings in winter 
and cool them in summer so as to maintain a moderate and nearly 
constant temperature. He can see that his dwellings have win- 
dows to let light and air pass in and out. He can have light at 
night and shade from intense light by day. He can have a sys- 
tem of pure water supply and drains or sewers to carry awaj^ 
his wastes. He can plan parks and playgrounds so that the city 
folk may have breathing spaces, as do their more fortunate neigh- 
bors in the smaller towns. He can see to it that people ill with 
*' catching " or communicable diseases are isolated or quarantined 
from others. Best of all, he is slowly learning to control the harm 
done by the tiny parasites, plant and animal, that cause and spread 
diseases. This care of the artificial environment is known as sani- 
tation, while the care of the individual for himself within the envi- 
ronment is known as hygiene. It will be the chief aim of this book 
to show girls and boys how they may become good citizens through 
the proper control of personal hygiene and sanitation. 

Summary. — We have found the life activities to be reactions 
to stimuli. As a result, plants and animals show definite responses 
that are called tropisms, and it appears that by means of these 
tropisms living things are better able to succeed in the world. 
They are, in a sense, creatures of the environment, for the sur- 
roundings determine the types which can live in any particular 
place. Plants and animals are also fitted or adapted to live in 
certain conditions by having their parts modified or changed so 
as to fit better the conditions in which they live. Man, how- 
ever, is able to change the conditions of his environment, or else to 
move to a more favorable one. In this sense, he is the most adapt- 
able of all living creatures, and as such, controls his living con- 


Problem Questions 

1. How does a living plant or animal differ from a stone? 

2. How are tropisms of value to plants ? To animals ? Give specific ex- 

3. How might animals do without light? Could they do without other 
factors of the environment ? 

4. How might movements help in the life of a plant or animal ? 

5. Give some examples of fitness or adaptation in a bean plant. In a tree. 
In a dog or cat. 

6. What do we mean by zonal distribution of plants and animals? Look 
this up in one of the books of reference. 

7. Under what unusual conditions do the Eskimos of the far North live ? 
How do they adapt themselves to their environment? 

8. Give instances of man's modification of his environment in your town. 
In your home. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Allen, Civics and Health. Ginn and Company. 

Hough and Sedgwick, Hygiene and Sanitation. Ginn and Company. 
Huntington and Gushing, Principles of Human Geography. John Wiley and 

Jordan and Kellogg, Animal Life. D. Appleton and Company. 
Loeb, Forced Movements, Tropisms and Animal Conduct. J. B. Lippincott 

Transeau, General Botany. World Book Company. 


Problems: To study insects — their structure, development, food, 
and homes. 

To study flowers — their structure and method of reproduction. 

To find out how insects and plants are adapted to aid each other; 
how flowers are pollinated. 

To learn how seeds are dispersed, and the importance of seed dis- 

Laboratory Suggestions 

A field trip. Object : to collect common insects and study their gen- 
eral characteristics ; to study the food and shelter relations of plants and in- 
sects. The pollination of flowers should also be carefully studied so as to 
give the pupil a general viewpoint as an introduction to the study of biology. 

Laboratory exercise. Examination of a simple insect, identification of parts, 
drawing. Examination and identification of some orders of insects. 

Laboratory demonstration. Life history of monarch butterfly and some 
other butterflies or moths. 

Laboratory exercise. Study of a simple flower : emphasis on the work of 
the essential organs ; drawing. 

Laboratory exercise. Study of the mutual adaptations in a given insect and 
a given flower, e.g. bumblebee and butter and eggs. 

Demonstration. Examples of insect pollination. 

Laboratory or field exercise. Study of seed dispersal. 

The Object of a Field Trip. — Many of us live in a city, where 
the crowded streets, the closely packed apartments, and the city 
playgrounds form our immediate environnient. Others of us live 
in a small town or in the real country. To understand the nor- 
mal environment of plants and animals we should go into the 
country. Failing in this, an overgrown city lot or a park will 
give us the environment as it touches some animals lower than 
man. We must remember that in learning something of the 
natural en-^dronment of other living creatures we may better 
understand our own environment and our relation to it. 





On any bright warm day in the fall we shall find insects swarming 
in a vacant lot or in a city park. Grasshoppers, butterflies alight- 
ing now and then on the flowers, brightly marked hornets, bees 
busily working over purple asters or goldenrod, and many other 
forms more or less hidden away on the leaves or stems of plants, 
may be seen. If we select for observation some partly decayed 
tree, we find it also inhabited. Beetles will be found boring 
through its bark and wood, while caterpillars (the young stages of 
butterflies and moths) are feeding on its leaves or building homes 
in its branches. Everywhere above, on, and under ground may 
be noticed small forms of life, many of them insects. Let us first 
see how we should go to 
work to identify some of 
the common forms we are 
likely to find on plants. 
Then a little later we shall 
find out what they are 
doing on these plants.^ 

How to tell an Insect. 
— A bee is a good ex- 
ample of the group of 
animals we call insects. 
If we examine its body 
carefully, we notice that 
it has three regions : a 
front part or head, a mid- 
dle part called the tho'rax, which is divided into three parts or seg- 
ments, and a hind portion, segmented and hairy, the dbdo'men. The 
three pairs of legs, which are jointed and provided with tiny hooks 
at the end, are attached to the thorax. How many joints can you 
find in each leg? Two pairs of delicate wings are attached to the 
upper or dorsal side of the thorax. The entire body has a tough 
covering or exoskeVeton composed of chitin (ki'tin), a substance 
chemically much like a cow's horn. This exoskeleton in the bee is 
partly covered with tiny hairs which form a vesture over the body. 
The muscles, which provide for movement, are fastened to the exo- 
skeleton, for there is no internal skeleton. If we watch the abdomen 

^ If the teacher desires, Chapter XXI may be used at this point. 

A bee viewed from the side. Notice the head, 
thorax, and abdomen. What other parts do you 
find? What structures, if any, are joined to each 
of these three body di\'isions? 


Head of a bee (side 
view) , showing com- 
pound eye. 

of a living bee, we notice it moves up and down quite regularly. 
The animal is breathing through tiny holes called spir'acles, placed 
along the sides of the thorax and abdomen. Bees have compound 
eyes composed of numerous units, each of which acts as a tiny 
camera. Bees are provided also with a pair of j ointed feelers called 
anten'nce. Wings are not found on all insects, 
nor is a vesture ; but the other structures just 
given are marks of the great group of animals 
we call insects. 

Forms to be looked for on a Field Trip. — 
Inasmuch as there are more than 450,000 
different species or kinds of insects, it is evi- 
dent that it would be a hopeless task for us 
even to attempt to recognize all of them. But 
we can learn to distinguish a few examples of 
the common forms that might be met on a 
field trip. In the fields, on grass, or on flowering plants we may 
find members from at least six of the twenty orders of insects. 
These may be known by the following characters : 

The order Hymeno'p'tera (membrane wings), to which the bees, 
wasps, and ants belong, is the only insect order of which some of 
the members are pro- 
vided with true stings. 
This sting is placed in 
a sheath at the extreme 
hind end of the abdo- 
men. Other structures, 
which show them to 
be insects, have been 
given above. 

Butterflies and moths 
will be found hovering 

over flowers. They belong to the order Lepidop'tera (scale wings). 
This name is given to them because their wings are covered with 
tiny scales, which fit into little sockets much as shingles are placed 
on a roof. The dust which comes off on the fingers when one catches 
a butterfly is composed of these scales. The wings are always large 
and usually brightly colored ; the legs are small, and one pair of 



Hymenoptera — bee. 




Youngkrya Qcoon 

Lepidoptera — stages in the development 
of the silk moth. 

them is often inconspicuous. These insects may be seen to take 
Hquid food through a long tubehke organ, called the prohos'cis, 
which they keep rolled 
up under the head when 
not in use. During de- 
velopment the young pass 
through a stage in which 
they are known as cater- 
pillars or larvce and feed 
on plants by means of a 
pair of hard jaws. 

Grasshoppers, found almost everywhere, and crickets, black 
grasshopper-like insects often found under stones, belong to the 
order Orthop'tera (straight wings). Members of this group may- 

usually be distinguished by their 
strong, jumping hind legs, by their 
chewing or biting mouth parts, and 
by the fact that the hind wings are 
folded up under the somewhat 
stiffer front wings. 

Another group of insects some- 
times found on flowers in the fall 
are flies. They belong to the order 
Dij^'tera (two wings). These in- 
sects are usually rather small and 
have a single pair of gauzy wings. 
Flies are of much importance to 
man because certain of their 
number are disease carriers. 

Bugs, members of the order 
Hemip'tera (half wings), have a 
jointed proboscis 
which is used for 
piercing and sucking. 
They are usually 
small and may or may not have wings. 

The beetles or Coleop'tera (sheath wings), often jj^^. 
mistaken for bugs by the uninformed, have two bedbug. 

Orthoptera — 1, cricket; 2, cock- 
roach ; 3, grasshopper. 


pairs of wings, but the first pair form hard covers meeting in a 
straight Hne in the middle of the back, the second pair of wings, 
when at rest, being covered by them. Beetles are frequently 

found on goldenrod blossoms. 
Try to discover members of 
the six different orders named 
above. Collect specimens 
and bring them to the labo- 
ratory for identification. 

Other animals which may be 

found are spiders, with four 

of walking legs, and 

Weevil. Ladybird. Calasoma beetle. 


centipedes and millepedes, both of which 

are wormlike and have many pairs of legs. 

Why do Insects live on Plants? — We 



have found insect life abundant on living green plants, some 
visiting flowers, others hidden away on the stalks or leaves of 
the plants. Let us next try to find out why insects live upon 
flowering green plants. 

The Life History of the Monarch Butterfly. — If it is possible 
to find some milkweed on our trip, we are quite likely to find hover- 
ing near, a golden brown and black butterfly, the monarch or milk- 
weed butterfly (Anosia plexippus). Its body, as in all insects, is 
composed of three regions. The female monarch frequents the 
milkweed in order to lay eggs ; she may be found doing this at 
almost any time from June until September. 

Egg and Larva. The eggs, tiny hat-shaped dots a twentieth of 
an inch in length, are fastened singly to the under side of milkweed 
leaves. Sorae wonderful instinct leads this butterfly to deposit ber 



eggs on the milkweed, for the young feed upon no other plant. The 
eggs hatch out in four or five days into rapidly growing wormlike 
caterpillars, each of 
which will shed its 
skin several times be- 
fore it is full grown. 
These caterpillars pos- 
sess, in addition to the 
three pairs of true 
legs, additional pairs 
of prolegs or cater- 
pillar legs. The ani- 
mal at this stage is 
known as a larva. 

Formation of Pupa. 
After a life of a few 
weeks at most, the 
caterpillar stops eat- 
ing and begins to spin 
a tiny mat of silk upon 
a leaf or stem. It at- 
taches itself to this 
web by the last pair 
of prolegs, sheds its 
skin again, and hangs 
there in the dormant stage known as the chrys^alis or pupa. 
This is a resting stage during which the body changes from a 

caterpillar to a butterfly. 

The Adult. After a week or more of 
inactivity in the pupa state, the outer 
skin is split along the back, and the 
adult butterfly emerges. At first the 
wings are soft and much smaller than in 
the adult. Within fifteen minutes to 
half an hour after the butterfly emerges, however, the wings are 
full-sized, having been pumped full of blood and air, and the insect, 
after her marriage flight, is ready to follow her instinct to deposit, 
her eggs on a milkweed plant. 

Monarch butterfly : adults, larvae, and pupa on their 
food plant, the milkweed. (From a photograph 
loaned by the American Museum of Natural History.) 



True fegs 
Caterpillar of 


moth, the 
squash borer. 


This life history gives us an example of what is known as a 
complete metamor' yJiosis or change of form. 

Plants furnish Insects with Food. — The insects which we have 
seen on our field trip feed on the green plants among which they 
live. Each insect has its own favorite food plant or plants, and in 
many cases the eggs are laid on the plant so that the young may 
have food close at hand. Some insects prefer the rotted wood of 
trees. An American zoologist, Packard, has listed 462 species of 
insects that live upon oak trees alone. Everyivhere animals are 

engaged in taking their 
nourishment from plants, 
and millions of dollars 
of damage is done every 
year to gardens, fruits, 
and cereal crops by in- 

All Animals depend on 
Green Plants. — ^ Insects 
in their turn are the food 
of birds ; cats and dogs 
may kill birds ; lions and 
tigers live on large de- 
fenseless animals such as 
deer or cattle. And 
finally, man eats the 
bodies of both plants 
and animals. But if we 
reduce this search for 
food to its final limit, we see that green plants provide all the food 
for animals. For the lion or tiger eats the deer which feeds upon 
grass or green shoots of young trees, and the cat eats the bird that 
lives on weed seeds or on insects that eat plants. Green plants 
supply the food of the world. 

Homes and Shelter. — On a field trip no one can fail to observe 
that plants often give animals a home. The grass shelters grass- 
hoppers and smaller insects which can be obtained by sweeping 
through the grass with an insect net. Some insects, such as the 
tent caterpillar, build their homes in the trees or bushes on which 

Trees with leaves destroyed by insects, in the 
Yosemite Valley, California. 


they feed, while others tunnel through the wood, making homes 
there. Spiders build webs on plants, often using the leaves for 
shelter. Birds nest in trees, and many other wild animals use 
the forest as their home. Man has learned to use many kinds of 
plant products to aid him in making his home, wood and various 
fibers being the most important of these products. 

What Animals do for Plants. — So far it has seemed as if green 
plants benefited animals and received nothing in return. We shall 
see later that plants and animals together form a balance of life on 
the earth and that each is necessary for the other. Certain sub- 
stances found in the body wastes from animals are necessary to the 
life of a green plant. 

Insects and Flowers. — Certain other problems can be worked 
out in the fall of the year. One of these is the biological inter- 
relation between insects and flowers. It is easy on a field trip to 
find insects lighting upon flowers. They evidently have a reason 
for doing this. 

The Use and Structure of a Flower. — It is a matter of common 
knowledge that flowers form fruits and that fruits contain seeds. 
Flowers, then, are not merely things of beauty, but are very impor- 
tant parts of plants. On our field trip we saw many flowers and 
noticed that they are of various shapes, colors, and sizes. It will 
now be our problem first to learn to know the parts of a flower, 
and then to find out how they are fitted to attract and receive 
insect visitors. 

The Floral Envelope. — The expanded portion of the flower 
stalk, which holds the parts of the flower, is called the receptacle. 
The green leaflike parts covering the unopened flower, when 
taken together, are called the ca'lyx. Each of these parts is a 
se'pal. The more brightly colored structures are the pet'als. 
Together they form the coroVla. The calyx and corolla together 
are called the floral envelope. 

The corolla is of importance in making the flower conspicuous. 
Frequently the petals or corolla have bright marks or dots which 
lead down to the base of the cup of the flower, where a sweet fluid 
called nectar is secreted by nectar glands. It is principally this 
food substance, later made into honey by bees, that makes flowers 
attractive to insects. 


The Essential Organs. — A flower, however, could have no 
sepals or petals and still do the work for which it exists. The 
essential organs of the flower are within the floral envelope. They 
consist of the sta'mens and pis' til (or pistils), the latter being in the 

center of the flower. 
The structures with the 
knobbed ends are called 
stamens. In a single 
stamen the boxlike part 
at the end is the anther; 
the stalk which holds 
the anther is called the 
fiVament. The anther is 
in reality a hollow box 
which produces a large 
number of little grains 
called pollen. Each 
pistil is composed of a 
rather stout base called 
the o'vary and a more 
or less lengthened por- 
tion rising from the 
ovary called the style. 
The upper end of the 
style, which in most 
cases is broadened, is 
called the stigma. The 
free end of the stigma 
usually secretes a sweet 
fluid in which grains of 
pollen from flowers of 
the same kind can grow. 
Insects as Pollinating 
Agents. — Insects often 
visit flowers to obtain pollen as well as nectar. In so doing they 
may transfer some of the poflen from one flower to another of the 
same kind. This transfer of pollen, called cross-pollination, is of 
the greatest use to the plant, as we shall see later. Sir John 


Cross sec f ion 
of ovary 

A simple flower, seen from above {A) and in sec- 
tion {B) ; and its separate parts. 

Sepdl Petal Stdmsn Mil 



Lub'bock tested bees and wasps to see how many trips they made 
daily from their homes to the flowers, and found that a wasp went 
out on 1 16 visits during a work- 

Coxa Coxd^ 


Coxa I ^fmur 


Tarsus, 5 parh 
Left froni le§ Middle le^ hind le^ 

Legs of a bee. 

pigment I 

ing day of 16 hours, while a bee 

made almost as many visits 

and worked almost as long as 

the wasp. It is evident that 

in the course of so many trips 

to the fields a bee must light 

on hundreds of flowers. 

Adaptations in a Bee. — When 

a plant or animal structure is 

fitted to do a certain kind of 

work, we say it is adapted to do that work. If we look closely 

at a bee, we find the body and legs more or less covered with tiny 

hairs, many of them branched. The joints in the legs of the bee 

adapt it for complicated movements ; the 
arrangement of stiff hairs along the edge 
of a concavity in one of the joints of the 
hindmost pair forms a structure called 
the pollen basket, adapted to hold pollen. 
Bees collect pollen and force it into this 
concavity by means of a pollen press (us- 
ually called the wax shears) located be- 
tween the tibia and metatar'sus of the hind 
pair of legs. (See figure above.) Pol- 
len obtained by the bee in this way is 
taken to the hive to be used as food. But 
while the insect is gathering pollen for 
itself, some is caught on the hairs and 
other projections on the body or legs and 
is carried from flower to flower. The 
value of this to a flower we shall see later. 
The Sight of the Bumblebee. — The 
large eyes located on the sides of the head 
are made up of a large number of little 

units, called ommatid'ia (sing, ommatidium) , each one of which is 

considered to be a very simple eye. The large eyes are therefore 

-Crystalline lens 
-Crystalline cone 

Xiorneal pigment 

■Retinal cell 


The compound eye is made 
of many units, each called an 


called the compound eyes. Some insects have only compound 
eyes, some only simple e^^s, but most insects have both. The 
simple ej^'es of the bee may be found by a careful observer be- 
tween and above the compound eyes. 

Insects can distinguish certain differences in color ; they can see 
moving objects, but the}^ do not seem to be able to make out form 
well. On the other hand, the}^ appear to have an extremely well- 
developed sense of smell. Insects can perceive at a great distance 
odors which to the human nose are not recognizable. Night-flying 
insects, especiall}^, find flowers by odor rather than by color. 

Mouth Parts of the Bee. — The mouth of the bee is adapted to 
take in pollen and nectar, and is used for some of the purposes for 
which man would use the hands and j 

fingers. The honeybee laps or sucks ^^ C^~^ 
nectar from flowers, it chews the pol- ^^Ejrf ibr md] 

^^mple eye 

Simpk eye 

The head of a bee, front and side views. 

Mouth parts of a grasshopper, 

for comparison with those of a 
bee. Ihr, labrum, or upper lip ; 
md, mandibles, the biting jaws; 
hyp, hypopharnyx, or tongue ; 
7713;, maxillae or under jaws; m.p. 
maxillary palps, sensory organs ; 
lab, labium or under lip — with 
l.p. labial palps. 

len, and it uses part of the mouth as a trow^el in making the honey- 
comb. The mouth parts may be seen in action by watching a bee 
on a well-opened flower. 

Butter and Eggs {Linaria vulgaris). — From July to October 
the very abundant weed called butter and eggs may be found 
especially along roadsides and in sunny fields. It bears a tall and 
conspicuous cluster of yellow and orange flowers. 

The corolla projects into a spur on the lower side; an upper 
two-parted lip shuts down upon a lower three-parted lip. The 
four stamens are in pairs, two long and two short. 



Certain parts of the corolla are more brightly colored than the 
rest of the flower. Butter and eggs is visited by bumblebees, 
which are guided by the orange lip to alight just where they can 
push their way into the flower. The bee, seeking the nectar se- 
creted in the spur, brushes its head and thorax against the stamens. 
It may then, as it pushes down after nectar, leave some pollen 
upon the pistil, thus ef- 
fecting self-pollination, 
which is the transfer of 
pollen from the anthers to 
the stigma of the same 
flower. Later, in visiting 
another flower of the same 
kind, the bee may leave 
some more of the pollen 
on the pistil of that second 
flower. Cross-pollination 
is the transfer of pollen 
from the anthers of one 
flower to the stigma of 
another flower of the same 
kind, — some say only if 
the two flowers are on dif- 
ferent plants. 

History of the Discov- 
eries regarding Pollination 
of Flowers. — Although the 
ancient Greek and Roman 
naturalists had some vague 
ideas on the subject of pol- 
lination, it was not until 
the first part of the nine- 
teenth century that a book appeared in which a German scientist, 
Conrad Spreng'el, worked out the fact that the structure of cer- 
tain flowers seems to be adapted to the visits of insects in that 
it offers easy foothold, sweet odor, and desirable food in the 
shape of pollen and nectar. Sprengel further discovered the fact 
that pollen can be and is carried by the insect visitors from the 

Diagram to show how a bee polHnates but- 
ter and eggs. A bumblebee, upon entering the 
flower, rubs its head against the long pair of 
anthers (A), then continuing to press into the 
flower so as to reach the nectar at N, it brushes 
against the stigma >S, thus pollinating the flower. 


anthers of a flower to its stigma. It was not until the middle of 
the nineteenth century, however, that an Englishman, Charles 
Darwin, applied Sprengel's discoveries on the relation of insects 
to flowers by his investigations concerning cross-pollination. The 
growth of the pollen on the stigma of the flower is a necessary step in 
the production of seeds, and thus of new plants. Many kinds of 
flowers are self -pollinated and do not do so well in seed production 
if cross-pollinated, but Darwin found that most flowers which 
are self-pollinated do not produce so many seeds, and that the 
plants which grow from their seeds are smaller and weaker than 

plants from seeds produced 
by cross-pollinated flowers 
of the same kind. He also 
found that plants grown 
from cross-pollinated seeds 
tend to vary more than 
those grown from self-pol- 
linated seed. This has an 
important bearing, as we 
shall see later, in the pro- 
duction of new varieties 
of plants. Microscopic ex- 
amination of the stigma 
at the time of pollination 
also shows that the pollen 
from another flower usu- 
ally germinates more rap- 
idly than the pollen which 
falls from the anthers of 
the same flower. This latter fact alone in most cases renders it un- 
likeh^ for a flower to produce seeds by its own pollen. Darwin 
worked for years on the pollination of many insect-visited flowers, 
and discovered in almost every case that showy, sweet-scented, 
or otherwise attractive flowers are adapted to be cross-pollinated 
by insects. He also found that, for flowers that are inconspicuous 
in appearance, often a compensation appears in an odor which 
renders them attractive to certain insects. The so-called carrion 
flowers, pollinated by flies, are examples, the odor in this case 

Two different -wild orchids. Flowers of this 
t>T3e were used hx Charles Darwin to work out 
iis theory of cross-pollination by insects. 


being like that of decayed flesh. Other flowers open at night and 
are white, besides having a powerful scent. Thus they attract 
night-flying moths and certain other insects. 

Other Devices to secure Cross-Pollination. — There are many 
other examples of adaptations to secure cross-pollination by means 
of the visits of insects. The mountain laurel shows a remarkable 
adaptation in having the anthers of the stamens caught in little 
pockets of the corolla. The weight of the visiting insect on the 
corolla releases the anther from the pocket in which it rests so that 
it springs up, dusting the body of the visitor with pollen. 

In some plants, self-pollination is prevented by certain devices, 
as in the primroses, in which the stamens and pistils are of different 
lengths in different flowers. Short 
styles and long filaments with high- 
placed anthers are found in some 
flowers, and long styles and short 
filaments with low-placed anthers in 
others. Pollination is most likely 
to be effected by some of the pollen 
from a low-placed anther reaching 
the stigma of a short-styled flower, 
or by the pollen from a high anther 
being placed upon a long-styled 
pistil. There are, as in the case of 
the spiked loosestrife, flowers hav- 
ing pistils and stamens of three 
lengths. Pollen grows best on pistils of the same length as the 
stamens from which it came. The stamens and pistil ripen at 
different times in some flowers. The " Lady Washington " gera- 
nium, a common house plant, shows this condition. Here cross- 
pollination must take place if seeds are to be formed.^ 

Special Adaptations between Flowers and Insects. — A very 
remarkable instance of insect help is found in the pollination of the 
yuc'ca, a semitropical lily which lives in deserts (to be seen in most 

The condition of stamens and pistils 
on the spiked loosestrife. 

1 For an excellent account of cross-pollination of milkweed, the reader is re- 
ferred to W. C. Stevens, Introduction to Botany. Orchids are well known to botan- 
ists as showing some very wonderful adaptations. A classic easily read is Darwin, 
On the Fertilization of Orchids. 

H. NEW CIV. BIOL. — 4 


The pronuba moth within the 
yucca flower. 

botanic gardens). In this flower the stigmatic surface is above the 
anther, and the pollen is sticky and cannot be transferred except 
by insect aid. This is accomplished in a remarkable manner. A 
little moth, called the pro'nuha, after gathering pollen from an 
anther, flies away with this load to another flower, there de- 
posits an egg in the ovary of the pistil, 
and then rubs its load of pollen over 
the stigma of the flower. When the 
egg hatches, the caterpillar feeds on 
some of the young seeds which have 
, ^ grown because of the pollen placed on 

/V^ y the stigma by the mother. Later it 

bores out of the seed pod and escapes 
to the ground, leaving the plant to de- 
velop the remaining seeds without 
further molestation. 

The fig insect {Blastophaga gros- 
sorum) is another member of the insect 
tribe that is of considerable economic importance. The fertili- 
zation of the flowers of the fig tree is brought about by a wasp 
which bores into the young fruit. By importing the wasps to 
California it was made possible to grow figs where for many years 
it was believed that the climate prevented them from ripening. 

Other Visitors to 
Flowers. — Among other 
useful pollen carriers for 
flowers are butterflies. 
Projecting from each side 
of the head of a butterfly 
or a moth is a fluffy 
structure, called thepaZp. 
This collects and carries 
a large amount of pollen, 
which is deposited upon 
the stigmas of other 
flowers when the butterfly pushes its head down into the flower 
tube after nectar. The scales and hairs on the wings, legs, and 
body of a butterfly also carry pollen. 

Humming birds, like bees, cross-pollinate some 
flowers while seeking nectar and insects. 



Flies, too, are agents in cross-pollination. Humming birds also 
are active agents in some flowers. Snails are said in rare in- 
stances to carry pollen. Undoubtedly, man and the domesticated 
animals frequently pollinate flowers by brushing past them while 
walking over the fields. 

Pollination by the Wind. — Not all flowers are dependent upon 
insects or other animals for cross-pollination. Many of the earliest 
spring flowers appear almost before the 
insects do, and are dependent upon 
the wind for carrying pollen from the 
stamens of one flower to the pistil of 
another. Most of our common trees, 
oak, poplar, maple, and others, are 
cross-pollinated by the wind. 

Flowers pollinated by the wind are 
generally inconspicuous and often lack 
a corolla. Their anthers are exposed 
to the wind and provided with much 
pollen, while the surface of their stigmas 
may be long and feathery. Such flowers 
may also lack odor, nectar, and bright 
color. Can you tell why? 

Imperfect Flowers. — Some flowers, 
especially those depending upon the 
wind for pollination, are imperfect ; 
that is, they lack either stamens or pis- 
tils. The corn plant is an example. 
Again, in some cases, imperfect flowers 
having stamens only are found on one 
plant, while those flowers having pistils 
only are found on another plant of the 
same kind. In such flowers, cross-pollination must of necessity 
follow. Many of our common trees are examples. 

The Necessity of Fruit and Seed Dispersal to a Plant. — 
We have seen that the chief reason for flowers, from the plant's 
standpoint, is to produce fruits Avhich contain seeds. The scatter- 
ing of fruits and seeds is absolutely necessary in order that colonies 
of plants may reach new localities. It is evident that plants 

The corn plant has staminate 
flowers at the top of the stalk 
and pistillate flowers at the 
side. (White circles were 
painted on the photograph, to 
show the location of the pistil- 
late flowers.) 


best fitted to scatter their seeds, or to place their fruits contain- 
ing seeds some Httle distance from the parent plants, are the ones 
which will spread most rapidly. A plant, in order to advance into 
new territory, must first get its seeds there. Plants which are best 
fitted to do this are the most widely distributed on the earth. 

Seeds and fruits transported by the wind : 1, milkweed ; 2, ash ; 3, maple ; 4, dan- 
delion ; 5, clematis ; 6, elm ; 7, basswood ; 8, thistle. 

How Seeds and Fruits are scattered. — Seed dispersal is accom- 
plished in many different ways. Some plants produce enormous 
numbers of seeds which may or may not have special devices to 
aid in their scattering. Most weeds are thus started in '^ pastures 
new." Some prolific plants, like the milkweed, have seeds with a 
little tuft of hairlike down which allows them to be carried by the 
wind. Others, as the omnipresent dandelion, have their fruits 

Fruits transported by animals: 1, beggar-tick; 2, tick trefoil; 3, Spanish needle i 
4, cocklebm- ; 5, sand bur ; 6, small flowered agrimony. 

provided with a similar structure, the pappus. Some plants, as 
the burdock and cocklebur, have fruits provided with tiny hooks 
which stick to the hair of animals, thus securing transportation. 
Most fleshy fruits contain indigestible seeds, so that when the 
fruits are eaten by animals the seeds are passed off from the 
body unharmed and may, if favorably placed, grow. Nuts of 
various kinds are often carried off by squirrels, buried, and for- 


gotten, to grow later. Such are a few of the ways in which seeds 
are scattered. All other things being equal, the plants best 
equipped to scatter seeds or fruits will drive out other plants in 
a given locality. Because of their adaptations these plants are 
likely to be very numerous, and for that reason some of them are 
likely to survive when unfavorable conditions come. Such plants 
are well exemplified in the weeds of the grass plots and gardens. 

The development of an apple. Notice that in this fruit additional parts besides 
the ovary (o) become part of the fruit. Certain outer parts of the flower, the sepals 
(s) and receptacle, become the fleshy part of the fruit, while the ovary becomes the 
core. Stages numbered 2 to 6 are in the order of development. 

Summary. — This chapter has brought out several important 
facts. First, plant life and animal life are closely interrelated, in 
that insects feed upon plants, make their homes in them, lay their 
eggs on their leaves or in their bodies, and in other ways depend 
on them. But the plant often gets something in return from this 
close association ; many flowers can form seeds only after pollina- 
tion by an insect visitor. Finally, although the plant may scatter 
its seeds without outside aid, we find many cases where animals are 
of assistance in this dispersal, again showing an interrelationship 
without which certain plants might be doomed to extinction. 

Problem Questions * 

1. What is a normal environment ? 

2. How would you distinguish an insect from other animals? 

3. What are the distinguishing characteristics of several orders of insects? 


4. \\Tiat is meant by a life historj^ ? 

5. How do plants benefit insects ? 

6. How do insects benefit plants ? 

7. "What uses have the parts of a flower? 

8. What kinds of pollination do we find and how is each brought about ? 

9. Name a flower and an insect and work out the interrelations they show. 

10. What agent other than insects carries pollen from one flower to another ? 
What adaptations do we find in wind-pollinated flowers ? 

11. Can j^ou give any instances of interrelationships between plants and 
animals which result in the scattering of seeds ? 

12. How has man made use of these interrelations? (Be specific.) What 
might man do to make more use of such interrelations ? Can you give any 
examples of "give and take" in human interrelationships? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Coulter, Barnes, and Cowles, A Textbook of Botany, Part II. American Book 

Dana, Plants and Their Children, pages 187, 255. American Book Companj^ 

Darwin, Different Forms of Flowers on Plants of the Same Species. D. Apple- 
ton and Company. 

Darwin, Fertilization in the Vegetable Kingdom, Chaps. I and II. D. Appleton 
and Company. 

Darwin, Orchids Fertilized by Insects. D. Appleton and Company. 

Densmore, General Botany. Ginn and Compan3\ 

Dickerson, Moths and Butterflies. Ginn and Company. 

Lubbock, Flowers, Fruits, and Leaves, Part I. The Macmillan Company. 

Lutz, Field Book of Insects. G. P. Putnam's Sons. 

Needham, General Biology, pages 1-50. Comstock Publishing Company. 

Stevens, Introduction to Botany. D. C. Heath and Company. 

Transeau, General Botany. World Book Company. 




Problems : To study cells in both plants and animals and find, 
the ways in which they are alike and different. 
To study the parts of a typical cell. 
To learn how cells produce other cells. 

Laboeatory Suggestions. 

Examination of cells from inside of cheek. 
Examination of cells from onion epidermis. 
Demonstration of elodea and protoplasmic movement. 
Demonstration of stained sea urchin or starfish egg to show chromosomes. 
Demonstration of dividing sea urchin or other eggs to show phases of 
cell division. 

Many Forms of Plants and Animals. — It is common knowledge 
that many kinds of green plants have roots, a stem, and leaves 
and bear at some time flowers, which give rise to fruits containing 
seeds. If a seed is planted, we know it will grow into a young 
plant of the same kind as produced it. But there are plants which 
do not form seeds, such as the mosses and ferns, and there are still 
others that are not green in color and may be too small to see with 
the unaided eye. 

Animals, too, as we know, are very diverse in size and appear- 
ance. A visit to a '' zoo " or a museum gives us some idea of the 
multitude of forms and their varied places of habitat. Insects, 
of which we know a little, are very numerous and very different 
from one another. And in animal life, as well as among the 
plants, we find forms so minute that we have to call the com- 
pound microscope to our aid in order to see them. 



How Cells were first found. — We have already found that we 
can distinguish life through its activities. A living organism is 
sensitive to stimuli, it moves, it grows by assimilating or changing 
over substances into the same chemical composition as itself, 
and it reproduces its kind. Is there any other way in which we 

can distinguish living from Ufe- 
less matter? 

A little over two hundred 
years ago, a Dutchman, Anton 
van Leeuwenhoek (la Ven-hook), 
made a collection of crude 
magnifying instruments that 
were the beginnings of our 
modern microscope. With these 
instruments he was able to see 
tiny organisms swimming in 
drops of pond water, and it is 
even thought that he first saw 
living bacteria. From this be- 
ginning a very complete knowl- 
edge has been gained concerning 
the building material of living 
A compound microscope is used to Organisms. An English doctor, 

magiiify small objects from about 40_to -^^^^^^ Hooke, examined COrk, 
500 tunes. The upright tube contams ' ' 

lenses. The object is placed on the stage which is the bark of an Oak 

thr/the"oS. too'ldnf ?own "Sto* tree, and found it was made up 
the lenses, one should see the object of tiny compartments, like little 

magnified in a clear light. ^^^^^^ ^j^-^j^ ^ie called Cells, a 

term which is now universally used for the unit of structure 
in living things. 

Protoplasm. — This name cell is not quite descriptive. Hooke 
saw the dead walls around the spaces that during the life of 
the plant contained living matter. But it was not until more 
recent times that biologists found that the content of the cell 
is the important living substance. This living material has been 
named pro'toplasm (Gr. protos, first; plasma, formative material). 
While we rarely see it or feel it, nevertheless observation has shown 
it to be always present where there is life. It is a sticky, semi-fluid 



Cell from 
stained nu- 

substance, somewhat like white of egg in consistency. Under the 
microscope it seems to be either granular or made of tiny bubbles 
floating in a more fluid medium, or it sometimes appears to be 
made up of delicate fibrils or threads, forming a network of infinite 
complexity. But it is always found making up the structure of 
living things, just as bricks make up the structure of 
a wall or a house. 

Structure of a Cell. — One of the easiest ways to 
obtain cells from your own body is to wash your 
hands carefully and then scrape the inside of your cheek 
with your clean finger nail. Place a tiny bit of the 
scrapings on a glass slide, add a drop of dilute blue 
fountain pen ink, place a cover glass ovsr it, and examine with a 
microscope. You will find a number of cells, more or less rounded 
in appearance, and more or less stained by the blue dye. A care- 
ful examination will show three distinct parts : an outer covering, 
which is the cell membrane, the cell body filled with protoplasm, 
and a more deeply stained portion of the protoplasm called the 

Plant cells are equally easy to see. If we 
peel the skin from one of the fleshy leaves 
forming an onion bulb, mount it in water to 
which is added a drop of dilute tincture of 
iodine, and examine it under a microscope, 
we find that this skin or epider'mis is also 
made of cells. Plant cells, however, differ 
from animal cells in that they have a deli- 
cate wood wall outside the membrane. 

If we examine the leaves of a green plant 
we find other structures within the cells. 
Examination of the delicate leaves of the 
elo'dea, a water plant used in aquariums, 
shows a more or less regular arrangement of the cells. But each 
cell shows many large spaces or vac'uoles, which are filled with a 
non-living fliiid instead of protoplasm. Forming a part of the 
protoplasm are many small ovoid bodies, most of which are green 
in color. These are the chloroplasts (klo'r6-plasts) or chlorophyll 
(klo'r6-fil) bodies (Gr. chloros, green; phyllon, leaf). We shall 


Cells of the epidermis of 
an onion. 


see later that they are of the utmost importance to each one of 
us, as it is by means of the action of the sun upon them that 
food is manufactured in the green parts of plants. 

In the elodea cells, an interesting phenomenon may be observed. 
The protoplasm in the cell body is seen to be constantly in motion, 
flowing slowly in the direction of the arrows shown in the diagram. 
This streaming of protoplasm is one of the manifestations of life 
within the cell. In many cells this movement may be observed 

/ f«^;*-.,3^^V--^ 


.j?|: ■■■;■,/.--• :^i- 


/ ^''-^^■■--1^ 

'/, ;^'. :-/^x.:.''* 

? ^f^W 


' iv :v^:a 

'■-,\:~- '.., V-. "9©- 


, W» :l.--^:«Hv 

;-^^-: Vy: .:^o-? 

•.«.,-■ ■■' •.■■:-o\---,- 

-»'• ^-^^%,.^ 

V »* : 11^^ ^'i 


1 « « -.■ ■ -'v^i;/*:- 

' v«t v :^-«- 

; :-^":^-:ii 

Cell wall 

Cell membrane 




A cell of elodea, a plant. The arrows 
show the "streaming" of the proto- 
plasm. White spots show vacuoles. 

.Cell membrane 





Diagram of a typical animal cell. In 
the nucleus, the dark thread-like struc- 
tures are stained chromosomes. 

and we have reason to believe that the protoplasm in most living 
cells is in motion, thus affording a circulation of the cell contents. 
If we now examine a specially prepared and stained cell, for ex- 
ample, the egg cell of a worm or a frog, we shall find that the nu- 
cleus, when stained with certain dyes, shows numerous small 
deeply stained bodies within it. These structures are called chro- 
mosomes (kro'm6-somz ; Gr. chroma, color; soma, body), or color- 
bearing bodies. The number of these chromosomes in each body 
cell of a given kind of plant or animal is always the same. The 
chromosomes are supposed to be the bearers of the qualities which 
can be handed down from parent to offspring; in other words, 



the inheritable quahties or characters which make the offspring 

liice its parents. 

Tissues and Organs. — The cells which form certain parts of 

the veins, the flat blade, or other portions of a leaf, are found in 

groups or aggregations, and are more or less alike in size and 

shape. Such a collection of cells is called a tissue. Examples of 

tissues in animals are the cells covering the outside of the body, 

forming the skin or epidermal tissue ; muscle tissue, which 

produces movement ; bony tissue, which forms the framework 

to which the muscles are ^ ■ , 


Falisade kyer 
A vein 
Spongy tissue 
Air spBce 

attached ; and there are 
many others. 

Collections of tissues 
which act together in the 
performance of work form 
organs. Such an organ is 
a leaf, made of supporting 
cells, green cells, spongy 
cells, etc., or the human 
arm, with its bony sup- 
porting tissue, its nerves 
and muscles, its blood ves- 
sels and connective tissue. 

How Cells form Others. 
— Cells grow to a certain 
size and then split into 
two new cells. In this 
process, which is of very 
great importance in the 
growth of both plants and 
animals, the nucleus divides first ; the halves separate and go to 
opposite ends of the cell. The chromosomes divide at the same 
time, each splitting lengthwise and the parts go in equal numbers 
to each of the two new nuclei formed from the old nucleus. In 
this way the matter in the chromosomes is divided equally between 
the two new nuclei. Then the rest of the protoplasm separates, 
and two new cells are formed. This process is known as cell 
division- The usual method of cell division is very complicated 

A vein with 
woody bundles 

Diagram of a small part of a leaf, partly in 
section, greatly magnified to show cells in this 



This type of cell division is called mitosis, and may be divided into four stages : 
the prophase, shown by 1, 2, 3, 4, 5 ; the metaphase (6) ; the anaphase (7, 8) ; and the 
telephase (9) . A material in the nucleus (n) called chromatin (ch) generally separates 
out into a thread (2), a band (3), and then breaks into parts, called chromosomes 
(4, cs). These arrange themselves at the center of the cell (5). Then the chromo- 
somes split lengthwise (6) and pass one half to each end of the cell as shown in 7 
and 8. A new nuclear membrane (n m) , and a new nucleolus {ns) — are formed 
in 9. Compare 9, the telephase, with 1, the prophase. Two little dots (1, c) in 
the cytoplasm are called centrosomes. These separate from each other but are 
connected by tiny threads, known as spindle fibers (3. st). Look for the centro- 
somes and spindle fibers in all the diagrams. 


in both plant and animal cells. You will note from the diagram 
that the division results in the placing of an equal number of 
chromosomes in each of the two new cells formed. 

Cells of Various Sizes and Shapes. — Plant cells and animal 
cells are of very diverse shapes and sizes. There are cells so large 
that they can easily be seen with the unaided eye ; for example, 
the root hairs of plants and eggs of some animals. On the other 
hand, certain cells, like the bacteria, are so minute that several 
million might be present in a few drops of milk. The forms of 
cells are extremely varied in different tissues ; they may have the 
shape of cubes, columns, spheres, or flat plates, or may be extremely 
irregular in outline. One kind of tissue cell, found in man, has a 
body so small as to be quite invisible to the naked eye, although 
it has a prolongation several feet in length. Such are some of the 
cells of the nervous system of man and large animals such as the 
ox, elephant, and whale. 

Varying Sizes of Living Things. — Plant cells and animal cells 
may live alone, or they may form collections of cells. Some plants 
are so simple in structure as to be formed of only one kind of cells. 
Usually living organisms are composed of many groups of different 
kinds of cells. Such collections of cells may form organisms so 
tiny as to be barely visible to the eye ; as, for instance, some of the 
small flowerless plants or many of the tiny animals living in fresh 
water or salt water. On the other hand, among animals, the bulk 
of the elephant and whale, and among plants, the big trees of Cali- 
fornia, stand out as notable examples. The large plants and ani- 
mals are made up of more, not necessarily larger, cells. 

Summary. — This chapter has shown us that the units of build- 
ing material in living things are called cells. These structures vary 
greatly in size, shape, and number ; but the size of an individual 
has little or no bearing on the size of the cells of which it is made. 

Animal cells are simply tiny bits of protoplasm, each containing 
a nucleus and surrounded by a delicate living covering called a 
membrane. Plant cells as a rule have a cellulose (woody) wall out- 
side the membrane. This is not alive, but is made by the activity 
of the protoplasm of the cell. Plant cells also contain large vacu- 
oles and, if green, chloroplasts (chlorophyll bodies). 

The nucleus is evidently the center of activity in the cell. When, 


through the assimilation of food materials, a cell has grown to a 
certain bulk, fixed in each form of animals and plants, the nucleus 
divides. The chromosomes divide, an equal number going to each 
new nucleus. Then the cell body divides, and two smaller cells 
result. This is cell division. 

Problem Questions 

1. Where and how does growth take place in the body of a plant or animal? 

2. In what respects are plant and animal cells alike? How are they dif- 
ferent ? 

3. Why do cells divide, instead of growing larger and larger in size? 

4. What is protoplasm ? Whj^ can we not see it in our bodies ? 

5. What changes take place in the cell when it divides ? Study the dia- 
grams carefully. 

6. What kinds of tissues can j^ou find in your own body without the use of 
the compound microscope ? Can you find any plant tissues ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Densmore, General Botany. Ginn and Company. 

Locy, Biology and Its Makers. Henry Holt and Company. 

Newman, Outlines of General Zoology. The Macmillan Company. 

Wilson, The Cell in Development and Heredity. The Macmillan Company. 




Problems : What causes a young plant to grow f 
What is the relation of the young plant to its food supply ? 
What are the outside conditions necessary for germination f 
What does the young plant do with its food supply f 
How is a plant or animal able to use its food supply f 
How does a plant or animal prepare food to use in various parts 
of the body? 

Laboratory Suggestions 

Laboratory/ exercise. Examination of a bean in the pod. Examination and 
identification of parts of a bean seed. 

Laboratory demonstration. Tests for the nutrients : starch, fats or oils, 
protein. Proof that such nutrients exist in beans. 

Home work. Test of various common foods for nutrients. Tabulate re- 

Home work. Char (partly burn) various kinds of common foods to find 
if carbon is present. 

Extra home work hy selected pupils. Factors necessary for germination of 
beans. Demonstration of experiments to class. 

Demonstration. Proof that materials are oxidized within the human body. 

Demonstration. Oxidation takes place in growing seeds. Test for oxida- 
tion products. Oxygen necessary for germination. 

Laboratory exercise. Examination of corn on the cob, the corn grain, lon- 
gitudinal sections of a corn grain stained with iodine to show that the embryo 
is distinct from the food supply. 

Demonstration. Test for grape sugar. 

Demonstration. Grape sugar present in growing corn grain. 

Demonstration. The action of diastase on starch. Conditions necessary 
for action of diastase. 

How Seeds are formed. — We have seen that the pollination of 
flowers results in the growth of the fruit containing the seeds of a 
plant. A bean pod is an example of one kind of fruit technically 
known as a leg'ume. Each seed in the pod contains a young plant 
or em^bryo. 




'Remains of sf-i^a 
and sf/le 



What makes a Seed grow. — The general purpose of the pages 
that follow will be to explain how the baby plant, or embryo, 

is able to grow into an adult plant. 
Two sets of factoi's are necessary for 
its growth : first, the presence of 
food to give the young plant a start ; 
second, certain stimulating factors 
outside the young plant, such as air, 
moisture, and warmth. 

If we open a bean pod, we find the 
seeds lying along one edge of the 
pod, each one attached to the inner 
wall by a little stalk. If we pull a 
single bean seed from its attach- 
ment, we see that the stalk leaves a 
scar on the coat of the bean: this 
scar is called the hi'lum. The thick 
outer coat {testa) is readily removed 
from a soaked bean, the delicate coat 
under it easily escaping notice. The 
seed separates into two parts ; these 
are called the cotyle'dons. If jqm 
pull apart the cotyledons very care- 
fully, you find certain other structures between them. The rod- 
like part is called the hypocofyl (meaning under the cotyledons). 
This will later form the 
root (and part of the stem) <:c^///^c/o/7^...=«..===— =...,,^re./a 

of the young bean plant. 
The first true leaves, very ^'"^'■/^^ 
tiny structures, are folded 
together between the coty- 
ledons, and are known as 
the plu'mule or epicot'yl 
(meaning above the cotyle- 
dons) . All the parts of the 
seed within the seed coats together form the embryo or young 
plant. A bean seed contains, then, a tiny plant protected by 
a tough coat. 


Bean pod and enlarged bean. 
The pistil of the flower of the bean 
plant becomes the fruit. The ovules 
develop into the seeds, and the egg 
cell becomes the embryo. 


A section through the bean shows that the 
embryo is made up of undeveloped leaves, the 
plumule ; an undeveloped shoot, the hypocotyl ; 
and nourishing structures, the cotyledons. 


Food in the Cotyledons. — The problem now before us is to find 
out how the embryo of the bean is adapted to grow into an adult 
plant. Up to this stage of its existence it has had the advantage 
of food and protection from the parent plant. Now it must begin 
the battle of life alone. We shall find in all our work with plants 
and animals that the problem of food supply is one of the most 
important problems to be solved by the growing organism. Let 
us see if the embryo is able to get a start in life (which many 
animals get in the egg) from food provided for it within its 
own body. 

What are Foods? — We have some knowledge of foods in our 
daily life. We eat meat, vegetables, fruits, and cereals ; we know 
that they have come from the bodies of plants or animals. That 
such foods are organic (of living origin) there can be no doubt. 
But we could not live without water, which is inorganic (of non- 
living origin) ; and experiments have proved that both plants 
and animals need certain compounds of iron, potassium, sodium, 
and other mineral salts, in order to live. It is evident, then, that 
foods may be organic or inorganic. 

Organic Nutrients. — Organic foods are made up of two kinds of 
substances, the nu'trients and the wastes or refuse. The organic 
nutrients are classed in four groups : 

Carhohy'drates are the simplest of the very complex chemical 
compounds called organic nutrients. They are composed of car- 
bon, hydrogen, and oxygen, the two latter elements in a propor- 
tion to form water. Starch (CeHioOs) and grape sugar (C6H12O6) 
are common examples of carbohydrates. 

Fats and Oils are, like carbohydrates, composed of carbon, 
hydrogen, and oxygen, but in some proportion which enables 
them to unite readily with oxygen. 

Proteins (pro'te-inz) are the most complex of all nutrients in 
their composition, and have, besides carbon, oxygen, and hydro- 
gen, the element nitrogen and minute quantities of other 

Vitamins (vi'td-mmz), a very important group which will be 
discussed in a later chapter. 

Test for Starch. — If we boil water with some laundry starch 
m a test tube, then cool it and add to the mixture two or three 

B. NEW CIV. BIOL. — 5 



drops of iodine solution/ we find that the mixture in the test tube 
turns purple or deep blue. It has been learned after many experi- 
ments that starch, but no other known substance, is turned purple 

Colors seen in test for starch, 

A, before; B, after, a 
grain of corn has been tested 
with iodine. 

or dark blue by iodine. Therefore, iodine solution is used as a 
test for the presence of starch. 

Starch in the Bean. — If we mash up a little piece of a bean coty- 
ledon which has been previously soaked in water, and test with 
iodine solution, the characteristic blue-black color appears, show- 
ing the presence of starch. If a little of the stained material is 
mounted in water on a glass slide under the compound microscope, 
we shall find that the starch is in the form of little ovoid bodies 
called starch grains (figure, page 60). The starch grains and 
other food products are made use of by the embryo. 

Test for Oils. — If a substance is rubbed on brown paper or is 
placed on paper and then warmed in an oven, the presence of oil 
will be shown by a translucent spot on the paper .^ 

Protein in the Bean. — Another nutrient present in the bean 
cotyledon is protein. Several tests are used to detect the presence 
of this nutrient. The following is one of the best known : 

Place in a test tube the substance to be tested ; for example, a 

1 Iodine solution is made by simply adding a few crystals of iodine to 95 per 
cent alcohol ; or, better, take by weight 1 gram of iodine crystals, i gram of iodide 
of potassium, and dilute to a dark brown coior in weak alcohol (35 per cent) or 
distilled water. 

2 The proportion of oil in beans is small, ft is better to try this test on a walnut. 



bit of hard-boiled white of egg. Pour over it a little strong (80 
per cent) nitric acid and heat gently. Note the color that 
appears — a lemon yellow. If a little ammonium hydrate is 






Colors seen in test for protein. There 
are two distinct steps in this test. 

A, corn grain before the test; B, when 
treated with nitric acid ; C, at completion 
of test, after treatment with ammonium 

added (preferably after washing the egg in water), the color changes 
to a deep orange. This change shows that a protein is present. 

If the protein is in a liquid state, its presence may be proved 
by heating, for when it coagulates or thickens, as does the white 
of an egg when boiled, protein in the form of an alhu'min is present. 

Another characteristic protein test easily made at home is 
burning the substance. If it gives off the odor of burning feath- 
ers or leather, then protein forms part of its composition. 

A test of the cotyledon of a bean with nitric acid and ammonium 
hydrate shows us the presence of protein. Beans are found by 
many tests to contain about 23 per cent of protein, 59 per cent 
of carbohydrates, and 2 per cent of oils. The young plant within 
a bean is thus shown to be well supplied with nourishment until 
it is able to take care of itself. In this respect it is somewhat like 
a young animal within the egg, — a bird or fish, for example. 

Germination of the Bean. — If dry seeds are planted in dry saw- 
dust or dry earth, they will not grow. A moderate supply of water 
must be given to them. If seeds are kept in a freezing tempera- 
ture or at a very high temperature, no growth will take place. 
A moderate temperature and a moderate water supply are most 
favorable for their development. 



Developed fiypocof /I- 

stages in the germination of the kidney bean. 

If some beans are planted so that we can make a record of their 

growth, we shall find the first signs of germination to be the break- 
ing of the testa and the 
pushing outward of the 
hypocotyl to form the 
first root, which grows 
downward. A later 
stage shows the hypoco- 
tyl forming an arch and 
dragging the bulky 
cotyledons after it. The 
stem, as soon as it is 
released from the 
ground, straightens up. 
The cotyledons open, 
and between them the 
budlike plumule or epi- 

cotyl grows upward, forming the first true leaves and all of the 

stem above the cotyledons. 

As growth continues, we 

notice that the cotyledons 

become smaller and smaller, 

until their food contents are 

completely absorbed into 

the young plant. The young 

plant now has roots and 

leaves and is able to care 

for itself and may be said 

to have passed through the 

stages of germination. 
What makes an Engine 

go. — If we examine the 

sawdust or soil in which the 

seeds are growing, we find 

it forced up by the growing 

seeds. Evidently work was 

done ; in other words, energy was released by the /Seeds. A 

familiar example of release of energy is seen in an engme. Coal 

Experiment to show the function of the 
cotyledons of the pea: a, plant with both 
cotyledons, b, with one removed, c, with both 
removed. A, at end of one week; B, at end 
of three weeks. 



is placed in the firebox and lighted, and the lower door of the 
furnace is opened so as to make a draft of air which will reach 
the coal. You know the result. The coal burns, heat is re- 
leased, causing the water in the boiler to make steam, the engine 
wheels to turn, and work to be done. Let us see what happens 
from the chemical standpoint. 

Coal, Organic Matter. — Coal is formed largely from dead 
plants, long ago pressed into its present hard form. It contains 
a large amount of the chemical element carbon. We have al- 
ready observed (page 11) one of the effects of the oxidation of 
carbon as proved by the limewater test. Let us now apply this 
test to the oxidation of food substances in our own bodies. 

Oxidation in our Bodies. — If we expel the air from our lungs 
through a tube into a bottle of limewater, we notice that the lime- 
water becomes milky. Evidently carbon dioxide is formed in our 
own bodies. In fact, the heat of the body (98.6° Fahrenheit) is due 
to oxidation within the body. Food is also oxidized within the 
human body to release energy for our daily work. In fact, all 
living things, both plant and animal, release energy as the result of 
oxidation of food within 
their cells. Let us prove 
this by an experiment 
with some peas. 

Food oxidized in Ger- 
minating Seeds. — If we 
take equal numbers of 
soaked peas, placed in 
two bottles, one tightly 
stoppered, the other hav- 
ing no stopper, both 
bottles being exposed to 
identical conditions of 
light, temperature, and 
moisture, we find that 
the seeds in both bottles 
start to germinate, but 
that those in the closed 
bottle soon stop, while those in the open jar continue to grow. 

Experiment that shows the necessity for air 
in germination. 


Why did not the seeds in the covered jar germinate? To 
answer this question, let us carefully remove the stopper from the 
closed jar and insert a lighted candle. The candle goes out at 
once. The surer test of limewater shows the presence of carbon 
dioxide in the jar. The carbon of the foodstuffs of the pea united 
with the oxygen of the air, forming carbon dioxide. Growth 
stopped as soon as the oxygen was exhausted. The presence of 
carbon dioxide in the jar is an indication that a very important 
process which we associate with animals rather than with plants, 
that of respiration, is taking place. The seed, in order to release 
the energy locked up in its food supply, must have oxygen, so that 
the oxidation of the food may take place. Hence a constant supply 
of fresh air is an important factor in germination. It is important 
that air should penetrate between the grains of soil around a 
seed. Frequent stirring of the soil makes it easier for air to reach 
the seed. 

Structure of a Grain of Corn. — Examination of a well-soaked 
grain of corn discloses a difference in the two flat sides of the 
grain. A light-colored area found on one surface marks the po- 
sition of the embryo ; the rest of the grain contains the food sup- 
ply. The interesting thing to remember here is that the food 
supply is outside of the embryo. 

^ A grain cut lengthwise perpendicular to 

^'^ the flat side and then dipped in weak iodine 
Cotyledon shows two distinct parts, an area containing 
Plumule considerable starch, the en'dosperm, and the 
embryo or young plant. Careful inspection 
shows the hypocotyl and plumule (the latter 
pointing toward the free end of the grain) 
Hypocotyl and a part surrounding them, the single coty- 

ledon (see figure). Here again we have an 
Section of corn grain, ^^ample of a fitting for future needs, for in 
this fruit the one seed has at hand all the food material necessary 
for rapid growth, although the food is here outside the embryo. 

Endosperm the Food Supply of Corn. — We find that the one 
cotyledon of the corn grain does not serve the same purpose to 
the young plant as do the two cotyledons of the bean. Although 
we find a little starch in the corn cotyledon, still it is evident from 



our tests that the endosperm is the chief source of food supply. 
The study of a thin section of the corn grain under the compound 
microscope shows us that the starch grains in the endosperm are 
large and regular in size. When the embryo has grown a little, an 
examination shows that the starch grains near the edge of the coty- 
ledon are much smaller and quite irregular, having large holes in 
them. We know that the germinating grain has a much sweeter 
taste than that which is not growing. This is noticed in sprouting 
barley or malt. We shall find later that, in order to make use of 
starchy food, a plant or an animal must in some manner change it 
to sugar. This change is necessary, because starch will not dis- 
solve in water, though sugar will ; and in fluid form substances can 
pass from cell to cell in the plant and thus go where they are needed. 
A Test for Grape Sugar. — Place in a test tube the substance to 
be tested and heat it in a little water so as to dissolve the sugar. 






Colors seen in test for grape sugar. 

A, a dry corn grain; B, a 
germinated corn grain, tested 
for grape sugar. 

Add to the fluid twice its bulk of Fehling's solution. ^ Heat the 
mixture, which should now have a blue color, in the test tube. If 
grape sugar ^ is present in considerable quantity, the contents of the 
tube will turn first a greenish, then a yellow, and finally a brick- 
red color. Smaller amounts will show kss decided red. No other 

^ Directions for making Fehling's solution, and Benedict's solution (page 60), will 
be found in Hunter's Laboratory Problems iii Civic Biology. 

2 Grape sugar, or glucose, is a simple kind of sugar found in many plants. 


food substance than grape sugar and certain other sugars will 
give this reaction.^ If Benedict's test is used, a colored precipitate 
will appear in the test tube after boiling, if grape sugar is present. 
Starch changed to Grape Sugar in the Corn. — That starch is 
changed to grape sugar in the germinating corn grain can easily 

be shown. First, cut length- 
wise through the embryos of half 
a dozen grains of corn and test 
with Fehling's solution to show 
that no grape sugar is present. 
Then test in the same way some 
lAfheBf Oaf Besn Corn Pes ^^^:^^^ ^j^^^ have just begun to 

Starch grains, magnified. • , i ^u •^^ ' 

germmate, and they will give a 
reaction showing the presence of sugar along the edge of the 
cotyledon and between it and the endosperm. 

Digestion. — This change of starch to grape sugar in the corn 
is due to a process called digestion. If you chew for a little time 
a bit of unsweetened cracker — which we know contains starch — 
it will begin to taste sweet, and if the chewed cracker is tested with 
Fehling's solution, some of the starch will be found to have changed 
to grape sugar. Here, again, the process of digestion has taken 
place. Both in the corn and in the mouth, this change is brought 
about by the action of chemical substances known as digestive 
ferments, or enzymes (en'zimz). Such substances have the power 
under certain conditions to change insoluble foods — solids — into 
soluble substances. The result is that foods which before diges- 
tion would not dissolve in water will dissolve after being digested. 

The Action of Diastase on Starch. — The enzyme found in the 
cotyledon of the corn, which changes starch to grape sugar, is 
called diastase (dfd-stas) . It may be separated from the cotyledon 
and is prepared by chemists for use in the form of a powder. 

To a little starch in half a cup of water add a very little diastase 
(1 gram) and put the vessel containing the mixture in a warm place, 
where the temperature will remain nearly constant at about 98° 
Fahrenheit. Testing part of the contents at the end of half an 
hour, for starch and for grape sugar, we find both of them present. 
If the rest of the mixture is tested the next morning, it will be 

1 Ordinary cane sugar or beet sugar will not give this reaction. 



found that the starch has been completely changed to grape sugar. 
Starch and warm water alone under similar conditions will not 
react to the test for grape sugar. 

Digestion has the Same Purpose in Plants and in Animals. — In 
our own bodies we know that solid foods taken into the mouth are 
broken up by the teeth and moistened by saliva. If we could 
follow that food, we should find that eventually it became part of 
the blood. It was made soluble by digestion, and in a liquid form 
was absorbed into the blood. Once a part of the body, the food is 
used either to release energy or to build up the body. 

A Summary of Nutrients and Their Tests 


Chemical Composition 



Contains Carbon (C) 

Hydrogen (H) 
Oxygen (0) 

Solution of iodine turns it dark 

Grape sugar 

Contains Carbon (C) 

Hydrogen (H) 
Oxygen (0) 

Forms brick-red precipitate 
when heated to boiling with 
Fehling's solution. 

Forms greenish, yellow, or red 
precipitate when boiled 
with Benedict's solution. 

Fats and oils 

Contain Carbon (C) 

Hydrogen (H) 
Oxygen (0) 

Leave a grease spot on paper 

after heating. 
May be extracted by mashing 

up substance with ether. 


Contain Carbon (C) 

Hydrogen (H) 
Oxygen (0) 
Nitrogen (N) 
and usually Sulphur (S) 
and other elements 

Turn yellow when heated with 
strong nitric acid, and then 
turn orange after addition 
of ammonium hydrate. 

Burning test (odor) 
Coagulation test (white of egg) 

Mineral matter 

Many elements, espe- 
cially Sodium (Na), 
Calcium (Ca), Iron (Fe) 

Remains as grayish ash after 
burning food in hot flame for 
long period. 


Hydrogen (H) 
Oxygen (0) 

Passes off from food when 
heated, as water vapor, and 
can be collected on cold 
metal or glass, as drops of 


Summary. — We have learned : 

1. That seeds, in order to grow, must possess a food supply 
either in or around their embryos. 

2. That this food supply contains starch, fats, and proteins. 

3. That this food supply must be oxidized before energy is 

4. That in cases where the food is not stored at the point where 
it is to be used, the food must be digested, so that it may be 
transported from one part of the plant to another. 

The life processes of plants and animals, so far, may be considered 
as alike ; they feed, take in oxygen, release energy, and grow. 

Problem Questions 

1. What conditions outside a seed are necessary to make it grow? What 
conditions inside the seed? 

2. What are organic foods? Inorganic foods? How do plants differ 
from animals in the use of food ? 

3. Of what use might food tests be to a boy or girl ? 

4. Compare an engine with a plant or an animal. In what ways are they 

5. How do corn grains and bean seeds differ? In what respects are they 

6. What is digestion? How is it brought about? Of what use is it to a 
plant ? To an animal ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Atkinson, First Studies of Plant Life. Ginn and Company. 

Coulter, Barnes, and Cowles, A Textbook of Botany, Part I. American Book 

Dana, Plants and Their Children. American Book Company. 
Densmore, General Botany. Ginn and Company. 
Duggar, Plant Physiology. The Macmillan Company. 
Hodge, Nature Study and Life, Chap. XXX. Ginn and Company. 
Lubbock, Flowers, Fruits, and Leaves. The Macmillan Company. 
Moore and Halligan, Plant Production. American Book Company. 
Transeau, General Botany. World Book Company. 
United States Department of Agriculture Year Books will give project refer- 



Problems : What is soil and what does a plant get from it? 
What determines the direction of growth of roots f 
How is a root fitted for the work it has to do f 
How do roots absorb water and soil salts? 
What is diffusion? What is osmosis? 

Laboratory Suggestions 

Laboratory or Home Experiment. How to determine the presence of organic 
matter in soil. 

Laboratory demonstration. To test the capacity of soils for holding moisture. 

Home experiment. To show the effect of gravity on a growing root. 

Laboratory demonstration. Structure of a root in cross section. 

Laboratory exercise. Roots and root hairs. 

Laboratory demonstration. To show that roots give off acid. 

Laboratory demonstration. To show diffusion and osmosis. 

Use of the Root. — If one of the seedlings of the bean is allowed 
to grow in sawdust and is given light, air, and water, sooner or 
later it will die. Soil is part of its natural environment, and the 
roots which come in contact with the soil are very important. It 
is the purpose of this chapter to find out just how the young plant 
is fitted to get what it needs from this part of its environment; 
namely, the soil. 

Composition of Soil. — As any one knows, the soil is composed 
of different substances in different localities. Contrast the black 
soil of Minnesota or Illinois with the sandy soil of Maine or 
California, or the red clay of Virginia. If we examine a small 
mass of garden soil carefully, we find that it is composed of numer- 
ous particles of varying size and weight. Between these particles, 
if the soil is not caked and hard packed, we can find tiny spaces, 
which are formed and enlarged when the soil is tilled. They allow 
the penetration of air and water. If we examine soil under the 




microscope, we find considerable water clinging to the soil particles 
and forming a delicate film around each particle. 

Under the microscope, also, most soils are seen to contain par- 
ticles of different kinds. Some are tiny pieces of rock, like those 
still being formed where solid rock is exposed to the weather. 
Rain, cold, and ice, working alternately with heat, chip off pieces 
of rock. These pieces in time may be worn smaller b}' the action 
of ^4nds, running water, and in some places by glaciers. These 
processes of soil making are aided by oxidation. A glance at crum- 
bling stones will give you an example of this, in the yellow oxide of 
iron (rust) disclosed. So by slow degrees the earth became covered 

Inorganic soil is being formed b\ 

Forests help to cover inorganic soil -^dth 
an organic coating. 

with a coating of what we call inorganic soil. Later, generation 
after generation of tiny plants and animals which lived in the soil 
died, and their remains formed the first organic materials of the soil. 

You are all familiar with the difference between so-called rich 
soil and poor soil. The dark soil contains more dead plant and 
animal matter, which forms the portion called humus. 

Humus contains Organic Matter. — It is eas}^ to prove that 
black soil contains organic matter, for if equal weights of care- 
full}^ dried humus and of soil from a sandy road are heated red- 
hot for some time and then reweighed, the humus will be found to 
have lost considerably in weight, and the sandy soil to have lost 
very little. The material left after heating is inorganic materiaL 
the organic matter having been burned out. 


Capacity of Soil for holding Water. — Soil containing organic 
materials holds water much more readily than inorganic soil, as 
a simple experiment shows. If we fill vessels of equal size (such 
as the one shown in the figure) with gravel, sand, barren soil, rich 
loam, leaf mold, and pulverized leaves — all dry — then pour equal 
amounts of water on them and measure all that runs through, the 
water that has been retained will represent the water 
supply that plants could draw on from such soil. 

Soil Water a Solution of Mineral Salts. — Water, 
as it passes through the soil, gradually dissolves 
very minute portions of the chemical compounds 
of which the soil is composed, so that soil water 
is really a dilute solution of mineral salts. 

Capillarity. — Water moves against the force of 
gravity by means of a physical phenomenon, that 
of capillar' ity. We know that water will rise against Apparatus for 
the force of gravity between two closely placed glass +^^?^? ^°^l ^^^^ 
plates or in a tube of very small bore. This is due 
to the fact that the particles or molecules of water are attracted to 
or adhere to the glass. Soil water adheres in the same way to the 
soil particles, and thus rises in the ground. 

Nitrogen in a Usable Form Necessary for Growth of Plants. — 
A chemical element needed by the plant to make protoplasm is 
nitrogen, but this element cannot be taken in an uncombined state 
from either soil water or air. It is usually obtained from the organic 
matter in the soil, where it exists with other substances in the form 
of ni'trates. Ammonia and other organic compounds which con- 
tain nitrogen are then changed by microscopic plants called 
bacteria, first into nitrites and then into nitrates, 

A Plant needs Mineral Matter to make Living Matter. — Liv- 
ing matter (protoplasm) , besides containing the chemical elements 
carbon, hydrogen, oxygen, and nitrogen, contains very minute 
proportions of other elements which make up the basis of certain 
minerals. These are calcium, sulphur, iron, potassium, magne- 
sium, phosphorus, sodium, and chlorine. 

That plants will not grow well without certain of these mineral 
substances^ can be proved by the growth of seedlings in a so-called 

1 See Hunter's Laboratory Problems in Civic Biology for list of ingredients. 



nutrient solution. If certain ingredients are left out of this 
solution, the plants placed in it will not live. 

/ "3 T 2 3 

Effect of the lack of certain chemical elements on the growth of plants. The 
three bottles contain (l) distilled water, (2) all the nutrients, (3) all the nu- 
trients except potassium nitrate. The second half, B, shows the same seedlings 
one week later than A. Add other bottles omitting in turn calcium sulphate, 
calcium phosphate, magnesium sulphate, sodium chloride, iron. Why the 
difference in amount of growth ? 

Root System. — If you dig up a young bean seedling and care- 
fully wash the dirt from the roots, you will see that a long root is 
developed as a continuation of the hypocotyl. This root is called 
the primary root. Other smaller roots which grow from the pri- 
mary root are called secondary, and 
the roots growing from the latter 
are called tertiary roots. Evidently 
the root acts as an anchor for 
the plant, but does it have other 

Downward Growth of Root. In« 
fluence of Gravity. — Most of the 
roots examined take a more or less 
downward direction. We are all 
familiar with the fact that the force 
we call gravity influences life upon 
this earth to a great degree. Does 
gravity act on the growing root? 
This question may be answered 

A root system, showmg primary, / , '^ 

secondary, and tertiary roots. by a simple experiment. 



Plant mustard or radish seeds in a pocket garden, place it on one 
edge, and allow the seeds to germinate until the root has grown to a 
length of about half an inch. Then turn it at right angles to the 
first position and allow it to remain for one day undisturbed. The 
root tips will be found to have turned in response to the change in 
position, and to point down again. That part of the root near 
the growing point is the one most sensitive to the change. Thi? 
experiment indicates that the roots are influenced to grow 
downward by the force of gravity and that the growing point is 
most responsive to this stimulus. Roots are positively geotropic. 

Root of a radish in a pocket garden that is turned in different positions at 
intervals of a day or more. 

Water a Factor which determines the Course taken by Roots. — 
Water, as well as the force of gravity, has much to do with the direction 
taken hy roots. If radish seeds germinate on the under side of a 
moist sponge suspended in the air, their roots will turn against 
gravity and cling to the wet surface of the sponge. Water is always 
found below the surface of the ground, but sometimes at a great 
depth. Most trees and all grasses have a greater area of surface 
exposed by the roots than by the branches. The roots of alfalfa and 
sugar beets, in our Western States, often penetrate the soil for a dis- 
tance of ten to twenty feet below the surface, until they reach that 
part of the soil which is always moist with underground water. 

The Fine Structure of a Root.^ — Let us now examine a root with 
the aid of the compound microscope, in order to see how it is 
fitted for the work of taking in and circulating soil water. We 
find the root to be made up of cells, the walls of which are rather 
thin. Over the lower end of the root is found a collection of cells, 
most of which are dead, loosely arranged so as to form a cap over 

^ Sections of tradescantia roots are excellent for demonstration of these structures. 



the growing tip. This is evidently an adaptation which protects the 
young and actively growing cells just under the root cap. In the 
body of the root a central cylinder of wood can easily be distin- 
guished from the surrounding cortex. In a longitudinal section 
a series of tubelike structures may be found within the central 
cylinder. These structures are made up of cells which have grown 
together end to end, the long axis of the cells running the length of 

Food passes 
down here 

up here 


Root cap 

Diagram of section of a root tip, 
showing structure. 

^ood/ bundle 

Diagram of a root tip, showing 
root hairs, greatly magnified. 

the main root. In their development these cells have grown to- 
gether in such a manner as to lose their small connecting ends, and 
now form continuous hollow tubes with rather strong walls. Other 
cells have developed greatly thickened walls, which give mechani- 
cal support to the tubelike cells. Collections of such tubes and 
supporting woody cells together make up what are known as 
fihrovas' cular bundles in the wood. 

Root hairs. — Careful examination of the root of one of the 
seedlings of mustard, radish, or barley grown in a pocket germi- 
nator shows a covering of tiny fuzzy structures, at most 3 to 4 




Roof- hairs 

Root hairs on a corn 


millimeters in length, called root hairs. They vary in length 
according to their position on the root, the most and the longest 
root hairs being found some distance back from the tip. They 
are outgrowths of the outer layer of the root, 
the epidermis, and are of very great im- 
portance to ths living plant. 

Structure of a Root Hair. — A single root 
hair examined under a compound microscope 
will be found to be a long, threadlike struc- 
ture, almost colorless in appearance. The 
cell wall, which is very flexible and thin, is 
made up of cellulose, through which fluids 
may easily pass. Clinging close to the cell 
wall is the protoplasm of the cell, the outer 
border forming a very delicate membrane. 
The interior of the root hair contains many 
vacuoles, or spaces, filled with a fluid called 
cell sap. Forming a part of the living proto- 
plasm of the root hair, sometimes in the hairlike prolongation and 
sometimes in that part of the cell which forms the epidermis, is 
found a nucleus. The nucleus, the membrane, and the rest of the 
protoplasm are alive ; the cell wall, formed by the living matter 

in the cell, is dead. The 
root hair is a living plant 
cell with a membrane and 
wall so delicate that water 
and dissolved mineral sub- 
stances from the soil can 
pass through them into the 
interior of the root. 

The Root Hairs take 
More than Water out of 
the Soil. — If a root con- 
taining a fringe of root hairs 
is washed carefully, it will be found to have little particles of soil 
still clinging to it. Examined under the microscope, these particles 
of soil seem to be cemented to the sticky surface of the root hair. 
The soil contains, besides a number of chemical compounds of 

•Soil particle 

Diagram of a root hair, with adjacent root 
cells and particles of soil. 



various mineral substances, — lime, potash, iron, silica, and many 
others, — a considerable amount of organic material. Acids of 
various kinds are present in the soil. These acids so act upon 
certain of the mineral substances that they become dissolved in 
the water which is absorbed by the root hairs. Root hairs also give 
off small amounts of acid, which assist in dissolving minerals. An 
interesting experiment may be shown to prove this. A solution of 

phenol phthaVein loses its color when an 
acid is added to it. If the roots of a 
growing pea are placed in a tube con- 
taining some of this solution, very 
sUghtly alkaline, the latter will soon 
change from a dehcate pink to a color- 
less solution. 

It is eas3^ to ssly that the delicate root 
hairs absorb water, but it is much more 
difficult to understand the process, be- 
cause it involves the understanding of 
certain physical phenomena. But since 
absorption is a process common to both 
plants and animal cells and is of vitsl 
importance, let us study it carefully. 

Diffusion. — We all know that certain 
substances, such as the odor of tobacco 
smoke or the perfumes of flowers, pass 
rapidly from the point where they are 
given off and tend to spread in all direc- 
tions through the air. The odor of the orange blossoms in California 
is a memor}' to those who have driven near the orange groves. 
Substances which will dissolve in liquids will also diffuse through 
the liquids. A httle powdered e'osin placed in a glass of water will 
soon make a glass of red ink, so completely does the eosin become 
dissolved and diffused through the liquid. In the diffusion of 
both gases and liquids particles of the substance pass from the 
place where they are most concentrated to where they are less 
concentrated, or lacking, the rate of travel being much slower 
in Hquids than in gases. 

Imbibition. — The passage of water from point to point by 

Effect of root hairs on phe- 
nolphthalein solution. The 
change of color indicates the 
presence of acid. 



capillarity does not account for soil water getting inside the cell. 
It has to go through the cellulose wall and the delicate membrane 
within. The walls of cells, like wood, absorb soil water readily by 
a process known as imbibition. This brings the soil water in con- 
tact with the cell membrane. Inside the cell membrane is a liquid 
which would diffuse freely with the soil water if the membrane 
were removed. But a membrane acts peculiarly toward diffusing 
substances. An experiment will help us to understand this. 

Osmosis. — If we carefully break away part of the shell of an 
egg so as to expose the delicate skin or membrane underneath, we 
have a picture of the relation of the cell membrane (like the egg 
skin) to the cell wall (like the egg shell) . If this egg is placed in a 
glass of cold water, within a short time the membrane will bulge 
out, showing that water has passed 
into the egg through the membrane. 
If, however, we test the water in the 
glass for protein, the organic sub- 
stance of which white of egg is 
composed, we shall find none. Evi- 
dently the egg membrane will per- 
mit the passage of water but not of 
protein. Such a membrane is said 
to be semi-yer'meable. It is this kind of membrane that surrounds 
plant and animal cells. It will permit certain substances such as 
water to pass through it readily in either direction, and it will per- 
mit certain substances in solution to pass less readily, while still 
other substances will not be permitted to pass through at all. 

Another experiment will help us. If we take a thistle tube, 
fill the lower end with a solution of grape sugar and water, then 
tie tightly over it an animal membrane (such as pig's bladder), 
and place the apparatus in water, as shown in the figure on the 
following page, we notice that after a very little time the fluid in the 
thistle tube begins to rise. Evidently water passes into the tube 
more rapidly than the substance inside can pass out. If we could 
see the separate particles, or molecules, of the water and of the 
solution of water and sugar, they would be found to arrange them- 
selves on each side of the membrane so as to cover it completely. 
But since the water molecules diffuse easily through the membrane 

Osmosis through the membrane of 
an egg. 








— ~_^— i| 

From the text on. pages 71, 72 explain why 
the water rises in one tube. 

and the sugar molecules do not diffuse easily, it will be seen that 
the inner side of the membrane does not present so much space 

for the diffusion of water par- 
ticles as does the other side. 
Hence the flow of water into the 
tube is more rapid than the flow 
out of the tube, and the water 
gradually rises in the thistle 
tube. This diffusion of water 
through a semipermeable mem- 
brane is known as osmo'sis. 
It will be seen that the greater 
flow of water particles or mole- 
cules is from the point of greater 
concentration of water to the 
point of lesser concentration of 
water; hence it is a true diffusion. And since the solution Tvithin 
the thistle tube is inclosed, the process causes a pressure by the 
solution within these closed walls. This is knowTi as osmot'ic pres- 
sure. This pressure, if continued, would burst the egg membrane 
in the experiment first noted and is a very important force in cir- 
culating the water in the root hair. 

Why the Root Hair absorbs Water and Soil Salts. — The wall of 
the root hair readily takes in water and dissolved soil salts by im- 
bibition. The outer edge of the protoplasm forms a semi-per- 
meable membrane, which, while allowing water and mineral salts 
in solution to diffuse toward the inside, will not allow the diffusion 
outward of the sugar and other soluble materials mthin the cell. 
Hence an inward flow of soil water is started. As soon as the outer 
cells have increased their holdings of soil water, an osmosis inward 
is started because the water tends to flow from the place of its 
greater concentration to the place of lesser concentration. Mineral 
salts in solution are carried along with the water so that the needed 
soil substances are carried along from cell to cell, until they reach 
the small tubes of the central cjdinder. Here other factors help 
the water up in the root ; of these, capillarity and the pull exerted 
by evaporation from the upper parts of the plant are believed to be 
the most important. We shall learn more about this later. 


Physiological Importance of Diffusion and Osmosis. — The 

processes of diffusion and osmosis are of great importance not only 
to a plant, but also to an animal. Foods are digested in the food 
tube of an animal ; that is, they are changed into a soluble form 
so that they may pass through the walls of the food tube and 
become part of the blood. The inner lining of part of the food 
tube is thrown into millions of little fingerlike projections called 
villi, which look somewhat, in size at least, like root hairs. These 
fingerlike processes are (unlike a root hair) made up of many cells, 
but they serve the same purpose as the root hairs, for they absorb 
liquid food into the blood. This process of absorption is not 
entirely understood, but is largely by diffusion and osmosis. With- 
out these processes we should be unable to use most of the food 
we eat. 

Summary. — This chapter has first shown us that rocks, the 
original earth material, have been broken down into the fragments 
we call inorganic soil. To this soil have been added, through the 
process of decay, the bodies of plants and animals which once 
covered the earth. Plants take out of the soil, water and soluble 
salts which are used by the plant in making food and eventually 
living matter. 

The structures by means of which the soil water is absorbed are 
called root hairs. These are elongated projections from cells of 
the outer covering of the root. 

The methods by which the fluids are taken into the root hairs 
and circulated through the cells of the root are known as diffusion 
and osmosis. Since the membrane of the root hair and other 
cells is semi-permeable, allowing the passage of some substances 
but not of others, a flow of soil water is established toward the in- 
side of the cell, because the membrane prevents the substances in 
the cell sap from flowing out. Thus osmotic pressure is established 
and roots are able to take in large amounts of water and soil salts. 

Problem Questions 

1. What are the chief differences between "poor" and "rich" soil? 

2. How is soil able to hold water? 

3. How are roots adapted to do their work? 

4. What part of the root is most sensitive to gravity? Prove your answer 
by experiment. 


5. Where do root hairs grow most abundantly? Where are they largest? 

6. How could you prove that root hairs give off acid? 

7. Distinguish clearly between diffusion and osmosis. 

8. What is meant by osmotic pressure and how might it be brought about ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Coulter, Barnes, and Cowles, A Textbook of Botany, Part II. American Book 

Duggar, Plant Physiology. The MacmiUan Company. 
Goodale, Physiological Botany. American Book Company. 
Transeau, General Botany. World Book Company. 


Problems: To study the structure of a leaf in order to find out how 
moisture is given off. 

To find the reaction of leaves to light. 

To study photosynthesis : the conditions and materials necessary, 
and the hy -product. 

To learn what other functions are performed hy leaves. 

Laboratory Suggestions 

Demonstration. The passage of fluids up the stem. 

Demonstration. Water vapor given off by a plant in sunHght. Loss of 
weight due to transpiration measured. 
Laboratory exercise. 

(a) Gross structure of a leaf. 

(6) Study of stomata and lower epidermis under microscope. 

(c) Study of cross section to show cells and air spaces. 
Demonstration. Reaction of leaves to light. 
Demonstration. Light necessary in starch making. 
Demonstration. Chlorophyll necessary in starch making. 
Demonstration. Air necessary in starch making. 
Demonstration. Oxygen a by-product of starch making. 

What becomes of the Water taken in by the Roots ? — We have 
seen that more than pure water is absorbed through the root hairs 
into the roots. What becomes of this water and the other sub- 
stances that have been absorbed? This question may be partly 
answered by the following experiments. 

Passage of Fluids up the Stem. — If young growing shoots 
from bean or pea seedlings are placed in red ink (eosin) and left 
in the sun for a few hours, some of the red ink will be found to 
have passed up the stem. 

Water given off by Evaporation from Leaves. — Take some well- 
watered potted green plant, as a geranium or hydrangea, cover the 
pot with sheet rubber, fastening the rubber close to the stem of 
the plant. Next weigh the plant with the pot. Then cover it 
with a tall bell jar and place the apparatus in the sun. Id a short 




time drops of moisture are seen to 
gather on the inside of the jar. If after 
a few hours we weigh the potted plant 
again, we find it weighs less than be- 
fore. Obviously the loss comes from 
the water vapor which has escaped from 
stem, or leaves, or both. 

The Structure of a Leaf. — In the ex- 
periment with the red ink and young 
shoots we shall find that the fluid has 
gone out into the skeleton or framework 
of the leaf. Let us now examine a leaf 
more carefully. It shows usually (1) a 
flat, broad Made, which may take almost 
any conceivable shape ; (2) a stalk, o:- 
pefiole, which spreads out into veins in 
the blade ; (3) stip'ules, a pair of out- 
growths from the petiole at its base. 
In many leaves the stipules fall off early. 
Some leaves are compound, that is, each 
of the little leaflike parts is in reality a 
section of the leaf blade which is so 

deeply indented that it is cut away to the midrib or central vein, 

as in the rose leaf shown in the figure below. 

The Cell Structure of a Leaf. — The outer covering of a leaf, on 

both the upper and the lower surfaces, is called the epidermis, and 

is composed of large (in 

dicotyledons, irregular) cells. 

The under surface of most 

leaves, as seen through a micro- 
scope, shows many tiny oval 

openings, called sto'mata (sing. 

sto'ma). Two guard cells, 

usually kidney-shaped, are 

found, one on each side of a 

stoma. By a change in the 

shape of these cells the stoma 

is made larger or smaller. 

Experiment to prove that 
water vapor is given off from a 
green plant. 

Compound leaf of rose, showing stipules si. 



Study of the leaf in cross section shows that the stomata 
open directly into air chambers which penetrate between and 
around the loosely arranged cells of spongy tissue composing the 
under part of the leaf. The upper surface of leaves sometimes 
contains stomata, but more 
often it does not. The under 
surface of an oak leaf of or- 
dinary size contains about 
2,000,000 stomata. Under the 
upper epidermis is a layer of 
green cells closely packed to- 
gether (called collectively the 
palisade layer) . These cells are 
more or less columnar in shape. 
Under them are several rows of 
the loosely placed cells called 
collectively the spongy tissue. If we happen to have a section 
cut through a vein, we find this composed of a number of tubes 
made up of, and strengthened by, thick- walled cells. The veins 
are evidently a continuation of the fibrovascular bundles of the 

stem out into the blade of 



Guard cell 


Stoma opening into yr 

air spdce in leaf / C 

Stomata open 

Stomata and guard cells, greatly 

Palisdde layer 

Spongy tissue 

Lower epidermis 


the leaf (figure, page 47). 

Evaporation of Water. — ■ 
During the day an enor- 
mous amount of water is 
taken up by the roots and 
' passed out through the 
leaves in the form of vapor. 
So rapid is this evaporation, 
or transpiration, in a small 
grass plant, that the water 
evaporated in a day may 
weigh more than the plant. It is estimated that nearly half a ton 
of water may be delivered to the air during twenty-four hours by 
a grass plot 25 by 100 feet, the size of the average city lot. It is 
estimated that a corn plant in the Central West passes out from 
its body more than forty gallons of water during its lifetime. 
Fields of wheat transpire nearly 20 per cent of the total rainfall on 

Diagram of section through the blade of a leaf, 
seen under a compound microscope. 


their area. The amount of water lost by plants through evapo- 
ration is many times more than the amount that goes into making 
food and living matter. 

Experiment to show through which surface of a leaf water vapor passes off: 
Remove two leaves of the same size from some large-leaved plant, as a mullein 
or a rubber plant. Cover the upper surface of one leaf and the lower surface of 
the other with vaseline. The leaf stalk of each should be covered with wax or vase- 
line, and the two leaves exactly balanced on the pans of a balance placed in a warm 
and sunny window. Within an hour the leaf having its upper surface covered with 
vaseline will show a loss of weight. 

Factors in Transpiration. — The amount of water lost from a 
plant varies greatly under different conditions. The humidity 
of the air, its temperature, and the temperature of the plant all 
affect the rate of transpiration. The stomata also tend to close 
under some conditions, thus helping to prevent evaporation. 
Recent experiments indicate that the plant probably has some con- 
trol over the stomata. The stomata are usually closed at night 
but remain open from shortly after sunrise until late in the 
afternoon. They begin to close in the middle of the afternoon, and 
thus decrease the amount of water lost in the latter part of the 
day. Plants droop or wilt on hot dry days because they cannot 
obtain water rapidly enough from the soil to make up for the loss 
through the leaves. Hairs on the leaf surface, waterproofing of 
outer cells, a decrease in leaf area, close grouping of leaves to 



prevent evaporation, the absence of leaves, as in the cactus, and 
the turning of leaves edgewise to light are all modifications which 
help to hold water in the body of the plant. 

Green Plants Food Makers. — We have already seen that green 
plants are the great food makers for themselves and for animals. 
We are now ready to learn how green plants make food. 

The Sun a Source of Energy. — We know the sun is the source 
of most of the energy that is received on this earth in the form of 
heat and light. Every one knows the power of a ^^ burning glass." 
Solar engines have not come into any great use as yet, because 
fuel is cheaper, but some day we undoubtedly shall harness the 
energy of the sun in everyday work. Experiments have shown 
that as much as 80 per cent of the radiant energy falling on 
certain green leaves is absorbed. Part of this energy is used by 
the leaf ; but part is changed to heat, raises the temperature of 
the leaf, and is lost to the air if the air is cooler than the leaf. 
Regulation of this temperature is obtained in much the same way 
as in our own bodies, by 
evaporation of water. We 
sweat; the leaf passes off 
water vapor, largely through 
the stomata. 

Effect of Light on Plants. 
— In young plants which 
have been grown in total dark- 
ness, no green color is found 
in either stems or leaves, the 
latter often being reduced to 
mere scales. The stems are 
long and more or less reclining. 

Two stages in an experiment to show that 
green plants grow toward the light. 

We can explain the changed 
condition of the seedling grown in the dark only by assuming that 
lack of light has some effect on the protoplasm of the seedling 
and induces the growth of the stem. If seedlings have been grow- 
ing on a window sill, or where the light comes in from one side, 
you have doubtless noticed that the stem grows toward the source 
of light and the leaves tend to arrange themselves so as to receive 
as much light as possible on their upper surfaces. The experiment 
pictured shows the effect of light very plainly. A hole was cut in 



one end of a cigar box and barriers were erected in the interior of 
the box so that the seeds planted in the sawdust received their hght 
by an indirect course. The young seedUng in this case responded 
to the influence of the stimuhis of hght so that it grew out finall}^ 
through the hole in the box into the open air. This growth of the 
stem to the light is of very great importance to a growing plant, 
because food making depends largely on the amount of sunlight 
the leaves receive. 

Effect of Light on Leaf Arrangement. — It is a matter of common 
knowledge that green leaves turn toward the light. Place growing 
pea seedlings, oxalis, or any other plants of rapid growth near 
a window which receives full sunlight. Within a short time the 
leaves will be found in positions to receive the most sunlight 
possible. Careful observation of any plants growing outdoors 
shows us that in almost every case the leaves are so arranged as 
to get much sunlight. The ivy climbing up a wall, the morning- 
glory, the dandelion, and the bur- 



dock, all show different arrange- 
ments of leaves, each presenting 
a large surface to the light. 
Leaves are often definitely ar- 
ranged, each fitting in between 
■^^ 'I others so as to present their 

H^^ J upper surface to the sun. Such 

an arrangement is known as a 
leaf mosaic. In the case of the 
dandelion, a rosette or whorled 
cluster of leaves is found. In 
the horse-chestnut, where the 
leaves come out opposite each 
other, the older leaves have 
longer petioles than the younger 
ones. In the mullein the entire plant forms a cone. The old 
leaves near the bottom have long stalks, and the little ones near 
the apex come out close to the main stalk. In every case each leaf 
receives a large amount of light. Other modifications of these 
forms may easily be found on a field trip or in a study of house 

A dandelion, showing a whorled 
ment of long irregular leaves. 


Starch made by a Green Leaf. — Remember that the upper 
surface of the leaf is placed toward the sun and that the leaf must 
be thought of as a solar engine. 

If we examine the palisade layer of the leaf, we find cells which 
are almost cylindrical in form. In the protoplasm of these cells 
are found a number of tiny green 
bodies, the chloroplasts or chlo- ^^^^-^ X^ 

rophyll bodies . If the leaf is placed 
in wood alcohol, we find that the 
bodies still remain, but that the 
color is extracted, going into the , 
alcohol and giving to it a beautiful 
green color. The chloroplasts are, 
indeed, simply part of the proto- 
plasm of the cell colored green. 

rrn IT r xi X J. Variegated leaves of tradescantia. 

Ihese bodies are oi the greatest 

importance directly to plants and indirectly to animals. The 
chloroplasts, by means of the energy received from the sun, manu- 
facture sugars and starches out of certain raw materials obtained from 
the soil and the air. These raw materials are soil water, which is 
passed up from the roots through the bundles of tubes into the 
veins of the leaf, and carbon dioxide, which is taken in through 
the stomata or pores. A plant with variegated leaves, as the 
tradescantia or " wandering Jew," makes starch only in the 
green part of the leaf, though these raw materials reach all parts 
of the leaf. 

The change of color of leaves in autumn seems to be due to 
loss of chlorophyll, plus the formation of a red pigment in the cells. 
It is probably not frost that causes leaves to turn but rather a 
combination of lower temperature with other factors. 

Light and Air Necessary for Starch Making. — If we pin strips 
of black cloth, such as alpaca, over portions of several leaves of a 
gi-owing hydrangea which has previously been placed in a dark 
room for a few hours, and then put the plant in direct sunlight for 
an hour or two, we are ready to test the leaves for starch. We 
remove the partly covered leaves, boil them to stop further 
changes, and extract the chlorophyll with wood alcohol (because 
the green color of the chlorophyll interferes with the blue color of 



the starch test). A test then shows that starch is present only in 
the portions of the leaves exposed to sunlight. From this experi- 
ment we infer that the sun has something to do with starch making 

Diagram of experiment to show that sunlight is necessary for starch making. 
Read the text carefully and then explain this diagram. 

in a leaf. The necessity of air for starch making may also easily 
be proved, for parts of leaves in a plant treal^d as in the previous 
experiment, if covered with vaseline, will be found to contain no 
starch, while the parts of the leaf without vaseline, but exposed 
to the sun and air, do contain starch. The part of the air used 
in starch making is carbon dioxide, which is always present in the 
atmosphere in very small amounts, less than 4 parts in 10,000 in 
fresh air. 

Air is necessary for the process of starch making in a leaf, not 
only because carbon dioxide gas is absorbed but also because the 
leaf is alive and must have oxygen in order to do its work. This 
oxygen it takes from the air. 

Comparison of Starch Making and Milling. — The manufacture 
of starch by the green leaf is not easily understood. The process 
has been compared to the work of a mill. In this case the mill is 
the chlorophyll of the leaf. The sun furnishes the motive power, 
the chloroplasts constitute the machinery, and soil water and 
carbon dioxide are the raw products taken into the mill. The 
manufactured product is starch,^ and a certain by-product 
(corresponding to the waste in a mill) is also given out. This 
by-product is oxygen. To understand the process better, we must 
refer to the diagram of a small portion of the leaf (page 77) . Here 
we find that the cells of the green layer of the leaf, under the upper 
epidermis, perform most of the work. The carbon dioxide is 

1 A simple sugar is manufactured and then transformed into starch. 


taken in through the stomata and reaches the green cells by way 
of the intercellular spaces and by diffusion from cell to cell. Water 
reaches the green cells through the veins. It then passes into the 
cells and there becomes part of the cell sap. The light of the sun 
easily penetrates the cells of the palisade layer, giving the energy 
needed to make the starch. This whole process is a very delicate 
one, and will take place only when external conditions are favor able « 



Compare the work of this part of a leaf (in starch making) with that of a mill. 

For example, too much heat or too little heat stops starch making 
in the leaf. This building up of starch, with the release of oxy- 
gen by the chloroplasts in the presence of sunlight, is called yho- 

Manufacture of Fats. — Inasmuch as tiny droplets of oil (or fat) 
are found inside the chlorophyll bodies in the leaf, we believe that 
fats, too, are made there, probably by a transformation of the 
starch already manufactured. 

Protein Making and its Relation to the Making of Living Mat- 
ter. — Protein is a part of the food which is necessary to form 

^ The process of photosynthesis is very complicated. It probably consists of 
three steps : first, the taking in of the raw materials, COo and H2O ; second, the rear- 
rangement of the elements within the green cells ; and third, the formation of 
very simple sugars, then of more complex sugars, and finally of starch. The 
process appears to be under the control of enzymes of different kinds, which cause 
these progressive changes to take place. Enzymes also change the sugars, which 
are carried to other parts of the plant for storage, into insoluble starch. 



protoplasm. It is present in the leaf and is found also in the 
stem and root. Proteins can be manufactm^ed in any of the cells 
of green plants where starches or sugars and certain salts are 
found, the presence of light not seeming to be a necessary factor. 
How they are manufactured is a matter of conjecture. The 
minerals brought up in the soil water form part of their composition, 

and starch or sugar gives three 
elements (C, H, and 0). The 
element nitrogen is taken up 
by the roots as a nitrate 
(nitrogen in combination with 
oxygen and some other 
element, usually with lime or 
potash) . Proteins are probably 
not made directly into proto- 
plasm in the leaf, but are stored 
by the cells of the plant and 
used when needed, either to 
form new cells in growth or 
to repair waste. ^\Tiile plants 
and animals obtain their food 
in different ways, they prob- 
ably make it into living sub- 
stance {assimilate it) in the 
same manner. 
Foods serve exactly the same purposes in 
they either are used to build living mattei 

A rock split by a growing tiee 

Functions of Food. 

plants and in animals 
or they are burned (oxidized) to furnish energy (power to do work) . 
If you doubt that a plant exerts energy, note how the roots of a 
tree bore their way through the hardest soil, and how^ stems or roots 
of trees often split the hardest rocks, as illustrated in the figure. 
Starch Making and its Relation to Human Welfare. — Leaves 
which have been in darkness show starch to be present soon after 
exposure to light. A corn plant may send almost half an ounce of 
reserve food into the ears in a single day. The formation of fruit 
and the growth of grain, potatoes, and other food crops, show the 
economic importance of the work of green leaves. Not only do 
plants make their own food and store it away, but they m^ke food 



for animals as well ; and the food is stored in such a stable form 
that it can be kept and sent to all parts of the world. Animals, 
herbivorous and flesh-eating, man himself, all are dependent upon 
the starch-making processes of the green plant for the ultimate 
source of their food. When we consider that in 1924 in the 
United States the total value of all farm crops was more than 
$12,000,000,000, and when we realize that these products came 
from the air and soil through the energy of the sun, we may realize 
why the study of plant biology is of great 

Green Plants give off Oxygen in Sun- 
light. — In still another way green plants 
are of direct use to animal life. During the 
process of starch making, oxygen is given 
off as a by-product. This may easily be 
proved by the following experiment. Place 
any green water plant in a battery jar 
partly filled with water,i cover the plants 
with a glass funnel, and mount a test tube 
full of water over the mouth of the funnel. 
Then place the apparatus in a warm sunny 
window. Bubbles of gas are seen to rise 
from the plant. After two or three hours 
of hot sun, enough of the gas may be 
obtained by displacement of the water to 
prove, by the rapid oxidation of a glowing 
splinter of wood in the gas, that oxygen is 

That oxygen is given off as a by-product 
by green plants is a fact of far-reaching 
importance. The green covering of the earth is giving to animals 
an element that they must have, while the animals in their turn 
are supplying to the plants carbon dioxide, a compound used in 
food making. Thus a widespread relation of mutual helpfulness 
exists between plants and animals. 

Experiment to show that 
oxygen is given off by green 
plants in sunlight. 

^ Water contains air in solution, including some carbon dioxide, but the amount 
may be too small. Immediate success with this experiment will be obtained if the 
water has been previously charged with carbon dioxide. 

H. NEW CIV. BIOL. — 7 


Respiration by Leaves. — All living things require oxygen. It 
is by means of the oxidation of food materials within the plant's 
body that the energy used in growth and movement is released. 
A plant takes in air with its oxygen largely through the stomata 
of the leaves, to a less extent through the lenticels in the stem, and 
through the roots. Thus rapidly growing tissues receive the 
oxygen necessary for them to perform their work. One of the prod- 
ucts of oxidation in the form of carbon dioxide is also passed 
off through these same organs. It can be shown by experiment 
that a plant uses up oxygen in the darkness ; in the light the amount 
of oxygen given off as a by-product in the process of starch making 
is much greater than the amount used by the plant. 

Summary. — From the above paragraphs it is seen that a leaf 
performs the following functions : (1) respiration, or the taking in 
of oxygen and passing ofT of carbon dioxide ; (2) photosynthesis, or 
starch making, with the incidental passing out of oxygen ; (3) for- 
mation of proteins, with their digestion and assimilation to form 
new tissues ; and (4) the transpiration of water. 

Problem Questions 

1. Why is it necessary for fluids to pass up a stem into the leaves? 

2. Of what use to man is the evaporation of water from leaves? 

3. Why does the amount of transpiration vary? 

4. Explain the process of photosynthesis. 

5. In what respects is this process of value to man? 

6. Should green plants be kept in a sick room at night? In the daytime? 

7. Do plants breathe ? How? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Calkins, Biology. Henry Holt and Company. 

Coulter, Barnes, and Cowles, A Textbook of Botany, Part II and Vol. II. 

American Book Company. 
Densmore, General Botany. Ginn and Company. 
Duggar, Plant Physiology. The Macmillan Company. 
Gager, Fundamentals of Botany. P. Blakiston's Son and Company. 
Goodale, Physiological Botany, pages 337-353 and 409-424. American Book 

Transeau, General Botany. World Book Company. 



Problems : To find out where plants store food and what use is 
made of it. 

To study the structure of stems and the passage of liquids up and 
down them. 

To find out how plants digest and assimilate food. 

Laboratory Suggestions 

Laboratory exercise. The structure (cross section) of a woody stem. 
Demonstration. To show that food passes downward in the bark. 
Demonstration. To show the condition of food passing through the stem. 
Demonstration. Plants with special digestive organs. 

The Circulation and Final Uses of Food in Green Plants. — We 

have seen that cells of green plants make food — especially the cells 
that are in the leaves. But all parts of the bodies of plants grow. 
Roots, stems, leaves, flowers, and fruits grow. Seeds are store- 
houses of food. We must now examine the stem of some plant in 
order to see how food is distributed, stored, and finally used in the 
various parts of the plant. 

The Structure of a Dicotyledonous or Woody Stem. — If we 
cut a cross section through a young willow or apple stem, we find 
it shows three distinct regions. The center is occupied by the 
spongy, soft pith ; surrounding this is found the rather tough wood, 
while the outermost area is hark. More careful study of the bark 
reveals the presence of three layers — an outer layer, a middle 
green layer, and an inner fibrous layer. The inner layer is made 
up largely of tough fiberlike cells known as hast fibers. The most 
important parts of this inner bark, so far as the plant is concerned, 
are many tubelike structures known as sieve tuhes. These are 
long rows of living cells, having perforated sievelike ends. 



Through these cells food materials pass downward from the upper 
part of the plant, where they are manufactured. 

In the wood will be noticed (see figure) a number of lines called 
med'ullary rays, or pith rays, radiating outward from the pith 

toward the bark. These are 
Cambium layer yy Annudl rings thin plates of pith which sepa- 
^hrdys rate the wood into a number 
of wedge-shaped masses . The 
masses of wood contain many 
elongated cells, which, placed 
end to end, form thousands 
of little tubes connecting 
the leaves with the roots. In 
addition to these are many 
thick- walled cells, which give 
strength to the mass of wood. 
The bundles of tubes with 
their surrounding hard-walled 
cells are the continuation of 
the bundles of tubes which 
are found in the root. In sec- 
tions of wood which have 
taken several years to grow, 
we find so-called annual rings. The distance between one ring 
and the next (see figure) usually represents the amount of growth 
in one year. Growth takes place from a layer of actively dividing 
cells, known as the cam'hium layer. This layer forms wood cells 
from its inner surface and bark from its outer surface. Thus new 
wood is formed as a distinct ring around the old wood. 

Use of the Outer Bark. — The outer bark of a tree is protective. 
The cells are dead, but the heavy woody skeletons prevent the evap- 
oration of fluids from within. The bark also protects the tree from 
attack of plants or animals which might harm it. Most trees are 
provided with a layer of corky cells. This layer in the cork oak is 
thick enough to be of commercial importance. 

There are small breathing holes known as len'ticels scattered 
through the surface of the bark. These can be seen easily in a 
young stem of apple, beech, or horse-chestnut. 

Diagram of a twig of box elder three years 
old, showing three annual growth rings. 
The radiating lines which cross the wood 
represent the pith rays or medullary rays. 



Proof that Food passes down the Stem. — If a freshly cut wil- 
low twig is placed in water, roots soon begin to develop from that 

part of the stem which is under 

water. If now the stem is girdled 

by removing the bark in a ring just 

above where the roots are growing, 

the latter will eventually die, and 

new roots will appear above the 

girdled area. The passage of food 

materials takes place in a downward 

direction just outside the wood in 

the layer of bark which contains the 

bast fibers and sieve tubes. This 

experiment with the twig explains 

why trees die when girdled so as to 

cut the sieve tubes of the inner bark. 

Many of the canoe birches of our 

forests are thus killed, girdled by 

thoughtless visitors. In the same 

manner mice and other gnawing 

animals kill fruit trees. To a much 

smaller extent food substances are 

conducted also in the wood itself, and food passes from the inner 

bark to the center of the tree by way 
of the pith rays. If the pith rays are 
tested for foods, it is found that much 
starch is stored in this part of the tree 

Structure of a Monocotyledonous 
Stem. — A piece of cornstalk examined 
carefully in cross section and longitudi- 
nal section shows us that the main bulk 
of the stalk is made up of pith, through 
which are scattered numerous stringy, 
tough structures called fihrovascular 
bundles. The latter are the woody 
bundles of tubes which in this stem pass 
through the pith and run into the leaves,. 

Experiment to show that food 
material passes down in the inner 

A broken cornstalk, with 
cross section (at left) : A^, 
node ; R, r, rind ; P, p, pith ; 
FV, fv, fihrovascular bundle. 


where (in young specimens) they may be followed as veins. The 
outside of the corn stem is formed of large numbers of fibrovascular 
bundles, which, closely packed together, form a hard, tough outer 
rind. Thus the woody material on the outside gives mechanical 
support to an otherwise spongy stem. 

Comparison in the Growth of a Dicotyledonous and a Monocoty- 
ledonous Stem. — In a young dicotyledonous stem, cut in cross 


Food made in 
leaves passes 
down fhrough 
— the inner bark 

Materials taken 
in by roof pass 
up the stem in 
this region 

Diagram to show the areas in a plant through which the raw food materials pass 
up the stem and food materials pass down. 

section, the woody bundles are arranged as a ring near the outer 
edge of the stem (see figure). These bundles grow both toward 
the outside and toward the center of the stem from an actively 
dividing layer of cells. This layer in older stems becomes a com- 
plete ring under the bark and is called the cambium layer. On the 
outside of the cambium layer is found the phlo'em, or portion con- 
taining the sieve tubes which bear elaborated food toward the 


roots. On the inside is found the xylem (zi'lem), or woody tubes 
that carry water upward. 

In the monocotyledonous stem the bundles are scattered, lack 
the cambium, and increase in number as the stem grows older. 
They contain sieve tubes on the inside and water-bearing tubes 
in their outer part. 

What causes Water to rise in a Stem. — • We have already seen 
that osmosis is responsible for getting water inside the root, and 
that the pressure exerted by this water {root pressure) is frequently 
capable of forcing fluids a considerable distance up a living stem. 
But during most of the year root pressure plays a very unimportant 
part in this phenomenon. It has been found that in small tubes, 
such as we find in wood, the cohesive force of molecules of water is 
very great. Also a very large amount of water is evaporated every 
day through the stomata. This, according to Ganong, averages 
about 50 grams per square meter of leaf surface in daylight and 
about 10 grams in darkness, almost half a ton of water being evap- 
orated from a large tree on a warm summer's day. This evapora- 
tion causes a pull on the volume of water in the fibrovascular 
bundles and is an important factor in the rise of fluids in stems. 

Digestion. — Much of the food made in the leaves is stored in 
the form of starch. But starch, being insoluble, cannot be passed 
from cell to cell in a plant. In our study of the root hair we found 
that substances in solution {solutes) will pass from cell to cell by 
diffusion. In our study of a growing seedling we found that a 
solid food substance, starch, was digested in the corn grain by an 
enzyme, thus becoming a diffusible substance which could pass 
from cell to cell. This process of digestion seemingly may take 
place in all living parts of the plant, although most of it is done in 
the leaves. In the bodies of all animals, including man, starchy 
foods are changed in a similar manner, but by other enzymes, into 
soluble grape sugar. 

The food material may be passed along in a soluble form until 
it comes to a place where food storage is to take place, and then it 
can be transformed again by the action of a reversible enzyme into 
an insoluble form (starch, for example) ; later, when needed by the 
plant in growth, it may again be transformed and sent in a soluble 
form through the stem to the place where it will be used. 


In a similar manner, protein seems to be changed and trans- 
ferred to various parts of the plant. Some forms of protein are 
soluble and others insoluble in Avater. White of egg, for example, is 
slightly soluble, but can be rendered insoluble by heating it so that 
it coagulates. Insoluble proteins are digested within the plant; 
how and where is but slightly understood. Soluble proteins pass 
down the sieve tubes in the bast and then may be stored in the 
bast or medullary rays of the wood in an insoluble form, or they 
may pass into the root, fruit, or seeds of a plant, and be stored 
there. This stored food becomes of immense value to mankind, 
for it forms not only our cereal, potato, and other crops, but also 
our fruits of all kinds. 

Plants with Special Digestive Organs. — Some plants have 
special organs of digestion. One of these, the sundew, has leaves 

which are covered on one 
side with tiny glandular hairs. 
These attract insects and later 
serve to catch and digest the 
nitrogenous matter of these in- 
sects by means of enzymes 
/^/ ^'# ' '.>. I poured out by the same hairs. 

§ i Another plant, the Venus's fly- 

Three modified leaves, which get nitro- trap, catches insects in a seusi- 

gen from captured insects: 1 pitcher ^^^^ j^^f ^^j^-^j^ £^1^3 ^^^ 

pJant; 2, sundew; 3, Venus s flytrap. i i i i • o '^ 

holds the msect fast until en- 
Z3anes poured out by the leaf slowly digest it. Still others, called 
pitcher plants, use as food the decayed bodies of insects which fall 
into their cuplike leaves and die there. These few plants are 
somewhat like those animals which have certain organs in the 
body set apart for the digestion of food. 

Summary. — The raw^ materials which have been absorbed by 
the roots pass through conducting tubes up the stem to the leaves, 
where they are manufactured into food. This food passes down 
the stem, as a liquid, in the sieve tubes, until it reaches a place 
where it is used to build tissue or is changed to a solid form and 

Summary of the Functions of Plants and Animals. — The processes 
which have just been described; with the exception of food making, 



are those which occur in the life of any plant or animal. Both 
plants and animals breathe; they oxidize their foods to release 
energy, carbon dioxide being given off as the result of the union of 
the carbon in the foods with the oxygen of the air (or of the air dis- 
solved in water) . Both plants and animals digest their food ; plants 
may do this in the cells of the root, stem, and leaf. Digestion 
must always occur so that food can be moved in a soluble condition 
from cell to cell in the plant's body, and it must take place in an 
animal for precisely the same reason. 

Assimilation. — The assimilation of foods, or making of foods 
into living matter, is a process about which very little is known. 
We know it takes place in the living cells of plants and animals. 
But how foods are changed into living matter is one of the mysteries 
of life which have not yet been solved. 

Excretion. — With the building and repair processes there is 
always waste, in both plants and animals. When living plants 
breathe, they give off carbon dioxide. In the process of starch 
making, oxygen might be considered the waste product. Water is 
evaporated from leaves and stems. The leaves fall and carry 
away waste mineral substances which they contain. 

Reproduction. — Finally, both plants and animals have organs 
of reproduction. We have seen that the flower gives rise, after 


Poppy Pine Street pohfo 

Section through seeds, showing embryos. 


pollination, to a fruit which holds the seeds. Each seed holds 
an embryo. Thus the young plant is doubly protected for a 
time and is finally thrown off with enough food to give it a start 
in life. In much the same way we shall find that animals re- 
produce, either by laying eggs each of which contains an embryo 
and food to start it in life or, as in the higher animals, by holding 


and protecting the embryo within the body of the mother until it 
is born, a helpless little creature, to be tenderly nourished by the 
mother until able to care for itself. 

Life History. — Ultimately both plants and animals grow old 
and die. Some plants, for example the pea or bean, live but a 
season ; others, such as the big trees of California, live for hundreds 
of years. Some animals, certain insects, exist as adults but a day, 
while the elephant is said to live almost two hundred years. The 
span of life from the time the plant or animal begins to grow until 
it dies is known as its life history (or sometimes its life cycle) . 

Pkoblem Questions 

1. What proof have we of the passage of water and food substances up and 
down the stem ? 

2. How do "monocot" and "dicot" stems differ? 

3. How does a stem get air? 

4. What causes water to rise against gravity in a stem? 

5. How and where are foods digested in plants ? 

6. Where are foods stored, and why ? 

7. What are the life processes of a green plant? 

8. Of what value are green plants to man ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Densmore, General Botany. Ginn and Company. 

Dana, Plants and Their Children, pages 99-129. American Book Company. 

Duggar, Plant Physiology. The Macmillan Company. 

Coulter, Barnes, and Cowles, A Textbook of Botany, Vol. I. American Book 

Gager, Fundamentals of Botany. P. Blakiston's Son and Company. 
Ganong, The Teaching Botanist. The Macmillan Company. 
Mayne and Hatch, High School Agriculture. American Book Company. 
Hodge, Nature Study and Life, Chaps. IX, X, XI. Ginn and Company. 
Transeau, General Botany. World Book Company. 
United States Department of Agriculture, Yearbooks, for project work. 





Problems: To study the simplest plants and animals and find in 
what ways they are alike and different. 

To find out where they live and how each performs some of the 
functions necessary to life. 

To understand what is meant hy the " cell as a unit.^' 

Laboratory Suggestions 

Laboratory study. Study of pleurococcus, or any unicellular green plant. 
Laboratory study. Study of amoeba or Paramecium. 
Laboratory study. To make a hay infusion. 

The Simplest Organisms. — The preceding division of this book 
has shown us that green plants are food-building organisms ; that, 
as such, they are of the greatest value to mankind. They are 
also living organisms, for they breathe, take in food, digest it, pass 
it through the body so that all parts may have nourishment and 
throw off waste materials. The fact that they manufacture the 
organic food substances for themselves makes them different from 

Some plants, however, are not green and so do not make their 
own food. Such are the many examples of fungi (fun-ji) which 
live in forests or fields, or which, in the form of common molds, are 
household pests. Our previous study of science has given us some 
knowledge of ^' germs " or bacteria, the lowest form of colorless 

As a matter of fact, it is extremely difficult for biologists to make 
any hard and fast distinction between the simplest plants and the 
simplest animals. There are many single-celled plants and many 
single-celled animals. If the cell is green, it is not always safe to 



call it a plant, because some animal cells appear to have small 
green plastids within them ; and the microscope reveals the pres- 
ence ot ehloroplasts within these animal cells. Also we might 
suppose that movement is an indication of an animal form. Here 
again we should find ourselves at fault, for there are many kinds 
of motile plant cells, while some animal cells are immotile. 

The best indication of plant or animal cell structure seems to be 
in the external layer of the cell. Plant cells usually have a cel- 
lulose wall in addition to a cell membrane, while animal cells usu- 
ally are surrounded by a membrane only. The internal structure 
of the two kinds of cells also shows some differences. 

Bacteria as Simple Plants. — We have seen that perhaps the 
simplest plants are the bacteria. They are so tiny that, whether 
» o in the form of a ball (coccus) , a rod (haciVlus) , or 

'0 ^^c<^' a spiral (spiriVlum) the details of cell structure 

are not well understood. They may have a 
^^' ' wall of nitrogenous material, and sometimes 

1 -y 9 • ■//• ^^ addition there is a sheath of gelatinous mat- 

^^ ter. A nucleus probably is present, although 

"iliahd bacilli ^^® nuclear matter may be scattered through 
the cell. Some bacteria have motile organs, 
in the form of threads of protoplasm called 
''^"//A c r ' c^7'^a, or longer ones called flageVla, with 
l\^ bacilli °''"^ which they move in fluids. They multiply 
rapidly by simply dividing in the middle to 

Forms of bacteria. /? x n t r t_i j-x' 

lorm two new cells. In unfavorable conditions 
they may form spores, which are resting cells with a heavy wall 
secreted about them. Such cells may resist dryness or heat, — 
even boiling, — for a considerable time. As we shall prove in 
later studies, bacteria, like animals, need organic food and favor- 
able conditions of the environment in order to grow. 

Pleurococcus. — A typical one-celled plant, however, would 
contain green coloring matter or chlorophyll, and would have the 
power to manufacture its own food under conditions giving it a 
moderate temperature, a supply of water, oxygen, carbon dioxide, 
and sunlight. Such a simple plant is the pleurococ'cus, seen on 
the shady side of trees, stones, and city houses. This plant would 
meet one definition of a cell, as it is a minute mass of protoplasm 



containing a nucleus. It is surrounded by a wall of a woody 
material formed by the activity of the living matter within the cell. 
It also contains a lobed mass of protoplasm which is colored 
green, the chloroplast. Such 
is a simple plant cell. 

A Hay Infusion. — An ex- 
ample of the close relation 
between plants and animals 
may be seen in the study of a 
hay infusion. If we place a 
wisp of hay or straw in a 
small glass jar nearly full of 
water, and leave it for a few 
days in a warm room, certain 
changes are seen to take place 
in the contents of the jar : The water gets cloudy and darker in 
color, and a scum appears on the surface. If some of this scum 
is examined under the compound microscope, it will be found to 
consist almost entirely of bacteria. These bacteria aid in the 
decay which, as the unpleasant odor from the jar testifies, is be- 

A spherkdl digs 

Pleurococcus. This one-celled green plant 
may live singly or in groups. 


A psramecJum 

Life in a late stage of a hay infusion. 

ginning to take place. Bacteria flourish wherever the food supply 
is abundant. The water within the jar has come to contain much 
of the food material which was once within the leaf of grass, — 
organic nutrients, starch, sugar, and proteins, formed in the leaf 
by the action of the sun on the chlorophyll of the leaf, and now 
released into the water by the breaking down of the walls of the 



cells in the leaf. The bacteria themselves release this food from 
the hay by causing it to decay. 

Where to find Paramecia. — If we examine the surface of a 
hsij infusion, we find a scum formed of bacteria, and a mass of 
whitish tiny dots collected along the edge of the jar close to the sur- 
face of the water. More attentive observation shows us that these 
objects move, and that they are never found far from the surface. 
They are one-celled animals of several species, but among them 
we are almost sure to find a slipper-shaped cell, the parame'cium. 
The Structure of a Paramecium. — The cell body is almost 
transparent and consists of semifluid protoplasm which has a 

granular, grayish appearance under the 

^j^Peiiide microscope. This protoplasm appears to 

^Contractile vacuole ^^ bounded by a very delicate peVlicle or 

covering through which project numer- 

Micronuchus ous delicate threads of protoplasm called 

Mouth cilia. The locomotion of the Paramecium 

\ ^^ - f^ood vacuole is caused by the movement of these cilia, 

. . , which lash the water like a multitude of 

. "- ,'"' ContracHle vacuole ^^^J ^^^^- The cilia also send particles of 

^ food along a groove into a funnel-like 

%/,i'^' opening, the gullet, on one side of the cell. 

A Paramecium. Once inside the cell body, the particles of 

food materials are gathered into little balls within the almost 

transparent protoplasm. These masses of food are inclosed in a 

little bubble-like area called a vacuole, containing fluid. Two larger 

vacuoles may be found; these are the contractile vacuoles; their 

purpose seems to be to pass off Hquid waste material from the cell 

body. This is done by pulsation of the vacuole, which ultimately 

bursts, passing fluid waste to the outside. Solid wastes are passed 

out of the cell through an a^nal opening, in somewhat the same 

manner. No breathing organs are seen, because diffusion of 

oxygen and carbon dioxide may take place anywhere through the 

cell membrane. The nucleus of the cell is not easily visible in 

living specimens. In a cell that has been stained it has been found 

to be a double structure, consisting of a large and a small portion, 

called, respectively, the macronucleus and the micronucleus} 

^ Some species of paramecia have two micronuclei. 






Reproduction of Paramecium. — Sometimes a Paramecium may 

be found in the act of dividing into two by the process known 

as fission. Each of the new cells contains half 

of the original cell. The original cell may thus 

form in succession many hundreds of cells in every 

respect like the original parent cell. A process 

which appears to stimulate reproduction is called 

conjugation. Of this more will be told later. 
Amoeba.^ — In order to understand more fully 

the life of a simple bit of protoplasm, let us take 

up the study of the amoe'ha, a type of the simplest 

form of animal life. Unlike the plant and animal 

cells we have examined, the amoeba has no fixed Paramecium dividing 

form. Viewed under the compound microscope, ^ 

it has the appearance of an irregular mass of granular protoplasm. 

Its form is constantly changing as it moves about. This is due to 

the pushing out of tiny pro- 
^^ '^^-^ '^ ""^"^ ^x-^^""^^ ^i jections of the protoplasm 

of the cell, called pseudopo- 
dia (su-d6-po'di-d ; false 

How an amcBba moves (side view). 



feet). The locomotion is accomplished by a streaming or flowing 
of the semifluid protoplasm. The pseudopodia push forward in 
the direction in which the animal is 
to go, and the rest of the body fol- 
lows. In the central part of the cell 
is the nucleus, a spherical structure, 
seen more easily when the animals 
are killed and stained. 

Although but a single cell, still the 
amoeba responds to the stimulus of 
food when it is near at hand. Food 
may be taken into the body at any 
point, the semifluid protoplasm sim- Pseudopodium. 

Living amoeba seen through a 
1 Amoebae may be obtained from the hay in- microscope, 

fusion, from the dead leaves in the bottom of 

small pools, from the same source in fresh-water aquariums, from the roots of duck- 
weed or other small water plants, or from green algae growing in quiet localities. 
No sure method of obtaining them can be given, except to procure them from some 
good supply house when needed. 





ply rolling over and engulfing the food material. Within the body, 
as in the Paramecium, the food becomes inclosed within a fluid 
space or vacuole. The protoplasm has the power to take out such 
material as it can use to form new protoplasm or to give energy. 
Circulation of food material is accomplished by the constant 
streaming of the protoplasm within the cell. 

The cell absorbs oxygen from the water by diffusion through its 
delicate membrane, giving up carbon dioxide in return. Thus the 
cell '^ breathes " through any part of its body covering. 

Waste nitrogenous products formed within the cell when work is 
done are passed out by means of a contractile vacuole. 

The amoeba, like other one-celled organisms, reproduces by the 
process of fission. A single cell divides by splitting into two others, 



AmcBba, showing the changes which take place during division of a cell. 

each of which resembles the parent cell, except that they are 
smaller. When these become the size of the parent amoeba, they 
in turn divide. This is an example of asexual reproduction. 

When conditions unfavorable for life come, the amoeba, like 
some one-celled plants, encysts itself within a membranous wall. 
In this condition it may become dried and be blown through the 
air. Upon return to a favorable environment, it begins life again, 
as before. In this respect it resembles the spore of a plant. 

The Cell as a Unit. — In the daily life of a one-celled animal we 
find the single cell performing all the vital activities which we 
shall later find the many-celled animal is able to perform. In the 
amoeba no definite parts of the cell appear to be set off to perform 
certain functions ; but any part of the cell can take in food, absorb 
oxygen, change the food into protoplasm, and excrete the waste 
material. The single cell is, in fact, an organism able to carry on 


the business of living almost as effectually as a very complex 

Summary. — This chapter has shown us that the simplest plants 
and animals are composed of a single cell, but that, nevertheless, 
they are organisms. Plant cells differ from animal cells in struc- 
ture and function. But the bacteria and other colorless plants are 
more like animals than plants, in that they do not make food, 
but destroy it. Some one-celled organisms, such as Paramecium, 
are complex in structure, while others, such as bacteria, are very 
simple. It is probable that bacteria are the lowest forms of life 

Problem Questions 

1. Why is a single cell considered an organism? 

2. How do single cells absorb food? Digest food? Are these processes 
different in plant and animal cells? (Look this up in some good reference 

3. List the characters of a number of plant and animal cells. How are 
they ahke and how different ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Calkins, Protozoa. Lemcke and Buechner. 

Hegner, Introduction to Zoology. The Macmillan Company. 

Needham, General Biology. Comstock Publishing Company. 

Needham and Lloyd, Life of Inland Waters. Comstock Publishing Company. 

Sedgwick and Wilson, General Biology. Henry Holt and Company. 

Ward and Whipple, Manual of Freshwater Biology. John Wiley and Sons. 

H. new civ. BIOL. — 8 



Problems: To determine the general biological relations existing 
between plants and animals, as shown in a balanced aquarium. 
To understand the meaning of symbiosis. 

Suggestions for Laboratory Work 

Demonstration of life in a "balanced" and in an "unbalanced" aquarium. 
Determination of factors causing balance. 

Demonstration of some examples of symbiosis. 

Study of a Balanced Aquarium. — Perhaps the best way for us 
to understand the interrelation between plants and animals is to 

study an aquarium in which 
plants and animals live and in 
which a balance has been es- 
tablished between the plant 
life on one side and animal 
life on the other. Aquariums 
containing green pond weeds, 
either floating or rooted, a 
few snails, some tiny animals 
known as water fleas, and a fish 
or two, if kept near a light win- 
dow, will show this relation. 

We have seen that green 
plants, in favorable conditions 
of sunlight, heat, moisture, 
and with a supply of raw food 
materials, give off oxygen as a 
by-product whfle manufacturing food in their green cells. We 
know the necessary raw materials for starch manufacture are 
carbon dioxide and water, while nitrogenous material is necessary 


A balanced aquarium. Explain the term 



for the making of proteins within the plant. In previous experi- 
ments we have proved that carbon dioxide is given off by hving 
things when oxidation occurs in the body. The crawHng snails 
and the swimming fish give off carbon dioxide, which is dissolved 
in the water ; the plants themselves, at all times, oxidize food within 
their bodies, and so must pass off some carbon dioxide. The green 
plants in the daytime use up the carbon dioxide obtained from the 
various sources and, with the water which they take in, manu- 
facture starch. While this process is going on, oxygen is given off 
to the water of the aquarium, and this free oxygen is used by the 
animals there. 

The plants are continually growing; but the snails and fish 
eat parts of the plants. Thus the plant life gives food to the 
animals within the aquarium. 
The animals give off certain 
nitrogenous wastes. These ma- 
terials, with other nitrogenous 
matter from dead animals and 
parts of the plants, form part of 
the raw material used for protein 
manufacture in the plant. This 
nitrogenous matter is prepared 
for use by several different kinds 
of bacteria which first break the 
dead bodies down and then give 
the material to the plants in the 
form of soluble nitrates. The 
green plants manufacture food, 
the animals eat the plants and give off carbon dioxide and nitro- 
genous waste, from which the plants in turn make food and living 
matter. The plants give oxygen to the animals, and the animals 
give carbon dioxide to the plants. Thus a balance exists between 
the plants and animals in the aquarium. Make a table to show 
this balance. 

Relations between Green Plants and Animals. — What goes on 
in the aquarium is an example of the relation existing between 
green plants and animals. Everywhere in the world green plants 
are making food which becomes, sooner or later, the food of animals. 

The carbon and oxygen cycle in the 
balanced aquarium. Trace by means 
of the arrows the carbon from the time 
plants take it in as CO2 until animals 
give it off. Show what happens to the 





This diagram shows that plants and 
animals on the earth hold the same re- 
lation to each other as plants and ani- 
mals in a balanced aquarium. Explain 
the diagram in your notebook. 

Man does not feed to a great extent upon leaves, but he eats 
many roots, stems, fruits, and seeds. When he does not feed 
directly upon plants, he eats the flesh of plant-eating animals, 

which in turn feed directly upon 
plants. And so it is the world 
over ; the plants are the food 
makers and supply the animals. 
Green plants also give to the 
atmosphere e^^ery day a very 
considerable amount of oxygen, 
which the animals use. 

The Nitrogen Cycle. — The 
animals in their turn supply much 
of the carbon dioxide that the 
plant uses in starch making. 
They also supply some of the nitrogenous matter used by the 
plants, another part being given the plants from the dead bodies 
of other plants, and still another part being prepared from the 
nitrogen of the air through the agency of bacteria which live 
upon the roots of certain 
plants. These bacteria are 
the only organisms that 
can take nitrogen from the 
air. Thus, in spite of all 
the nitrogen of the at 
mosphere, plants and ani- 
mals are limited in the 
amount available. And 
the available supply is used 
over and over again. Eaten 
in protein food by an ani- 
mal, it may be given off 
as nitrogenous waste, get 
into the soil, and be taken 
up by a plant through the 
roots. Eventually the ni- 
trogen forms part of the food supply in the body of the plant, 
and then may become part of its living matter. When the 

Nitrogen from air 


Bacteria which take nitrogen from the air 
and put it into a usable form, are found in 
nodules on the roots of certain plants. 



plant dies, the nitrogen is returned to the soil, 
nitrogen is kept in circulation.^ 

Thus the usable 

Carbon dioxide 
I (CO2) 

Carbon dioxide 
I (CO2) 



with chlorophyll 

buildup complex 

organic substances 

They store up 

energy from the sun 

in the process 



and plants without 


I ^°^^. [which tear down complex! Ammonia 
orgam I organic substances 1 (NH3) 
food of \ , , ' 

^ and set free energy 

in the process in 
form of heat 

Energy from sun. Energy set free 

as heat. 
The relations between green plants and animals. 

Symbiosis. — We have seen that in the balanced aquarium 
the animals and plants, in a wide sense, form a sort of unconscious 
partnership. The living together of different organisms for mutual 
advantage is called symhio'- 

Animal Life 

qsing Bacteria 

sis. Some animals thus 
combine in a close part- 
nership with plants ; for 
example, the tiny animal 
known as the hydra with 
certain of the one-celled 
algae. Similarly, some 
animals live together sym- 
biotically, as witness the 
sea anem'ones living on 
the hermit crab, seem- 
ingly protecting it and 

being carried by the crab to where food is plentiful. If we accept 
the term symbiosis in a wide sense, all green plants and animals 
live in this relation of mutual give and take. The interrelation- 

1 A small amount of nitrogen gas is returned to the atmosphere by the action of 
the decomposing bacteria on the ammonia compounds in the soil. (See figure of 
nitrogen cycle.) 

Nitric Bacteria 

The nitrogen cycle. Trace the nitrogen from 
its source in the air until it gets back again 
into the air. 


ships of insects and flowers are another example of a symbiotic 
partnership if we use the term in its widest and best sense, as, 
indeed, is the give and take in our whole social life. Everyday 
life in a community or in a household must be give and take ; 
we must each sacrifice for others if we expect to have them do the 
same for us. The sacrifices made by parents must be matched in 
equal willingness to help on the part of the children if our social 
life is to continue. Thus we see that much of the foundation of 
society is built on this idea of mutual helpfulness. 

Summary. — Just as plants and animals in a balanced aquarium 
show a relationship of give and take, so plants and animals on the 
earth show this same relation. The living together of organisms 
of different kinds for mutual helpfulness is called symbiosis and is 
shown in an exact way in some forms of animal life, such as the 
hermit crab and sea anemone. But the fundamental idea is at 
the basis of a happy home life and the life of society. 

Problem Questions 

1. Can you make a balance sheet illustrating the relationg existing in a 
balanced aquarium ? 

2. What would be the condition of the balance sheet if the aquarium were 
put in a dark room ? If several extra snails and fish were introduced ? 

3. What are meant by the oxygen cycle, the carbon cycle, the nitrogen 
cycle? Make diagrams to illustrate. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Downing, Our Living World: A Source Book of Biological Nature Study. Uni- 
versity of Chicago Press. 

Eggelin and Ehrenberg, The Fresh Water Aquarium. Henry Holt and Com- 

Needham, General Biology. Comstock Publishing Company. 

Needham and Lloyd, Life of Inland Waters. Comstock Publishing Company. 

Ward and Whipple, Manual of Freshwater Biology. John Wiley and Sons. 

Woodruff, Foundations of Biology. The Macmillan Company. 



Problems: To understand what is meant by physiological division 
of labor. 

To learn the functions performed by the higher animals. 

To obtain a general understanding of the parts of the human machine 
and their uses. 

Laboratory Suggestions 

Exercise. Adaptations in a living frog. Comparison of external organs with 
homologous structures in man. 

Demonstration. Review to show that the human body is a complex of cells. 

Demonstration, by means of (a) human skeleton and (5) manikin, to show 
the position and gross structure of the chief organs of man. 

The Needs of Living Things. — We have already found that the 
primary needs of plants and animals are the same. Both need 
food. Both need to digest their food and to have it circulate in a 
fluid form to the cells where it will be used or stored. Both need 
oxygen so as to release the energy locked up in food. And both 
need to reproduce if their kind is to be continued on the 
earth. What is true of plants and animals is true of man, so far 
as his primary physical needs are concerned. 

The Needs of Simple and Complex Animals the Same. — The 
simplest animal, a single cell, has the same needs as the most 
complex. The Paramecium feeds, digests, oxidizes its food, and 
releases energy. It is the cells in the body of a worm or a fish 
or a frog that use food and do work. The cells of the human body, 
built up into tissues, have the same needs and perform the same 
functions as the cell body of the Paramecium. It is the cells of 
the body working together in gi'oups as tissues and organs that 
make the complicated actions of man possible. 




Physiological Division of Labor. — If we compare the amoeba 
and the Paramecium, we find the latter a more complex organism 
than the former. An amoeba may take in food through any part 
of the body ; the Paramecium has a definite gullet. The amoeba 
may use any part of the body for locomotion; the Paramecium 
has definite parts of the cell, the cilia, fitted for this work. Since 
the structure of the Paramecium is more complex, we say that it is 
a '^ higher " animal that the amoeba. 

As we look higher in the scale of life, we invariably find that 
certain parts of a plant or animal are set apart to do certain work, 
and only that work. Just as in a community of people there are 
some men who do rough manual work, others who are skilled work- 
men, some who are shopkeepers, and still others who are profes- 
sional men, so among plants and animals, wherever collections of 
cells live together to form an organism, there is division of labor, 
some cells being fitted to do one kind of work, while others are 
fitted to do work of another sort. This is called physiological 
division of labor. 

Enlarged views and enlarged lengthwise section of the hydra, a very simple ani- 
mal which shows slight division of labor: 1, hydra extended; 2, contracted; 
3, diagram of section. 

Division of Labor in Simple Animals. — In the hydra, a tiny 
simple animal found in fresh-water ponds or streams, the body is 
like an elastic bag, with an opening at one end. This opening, 



the mouth, is surrounded by a circle of tentacles, delicate organs 
which aid in getting food. There are only two layers in the body : 
the outside layer of cells is primarily protective ; the inner layer 
is chiefly digestive in function, though movement, locomotion, 
sensation, and reproduction are taken care of by various types 
of cells. Here, in other words, physiological division of labor is 
simple and the body structures also are simple. In so-called 
" higher " animals, as in a fish, frog, or bird, the organs are more 
complicated as division of labor becomes more specialized. In 
the human arm, an organ fitted for certain movements, think of 
the number of tissues and the complicated actions which are 
possible. The most extreme division of labor is seen in the or- 
ganism which has the most complex actions to perform, with each 
organ fitted for its own particular work, which it does quickly 
and well. 

Division of Labor in the Vertebrate Group ; the Frog. — Al- 
though we are interested chiefly in a study of man, because we wish 
to prepare ourselves for efficient citizenship, it is easier to study in 
the laboratory some small animal that resembles man in general 
structure. Such an animal is the frog, for it is a typical representa- 
tive of the vertebrate or backboned animals, and it is easy to obtain 
and to handle. 

The frog's internal organs are somewhat like those of man. 
Thus the frog has lungs, a heart, a stomach, intestine, various 
glands, etc. 

You will notice that the appendages of a frog have the same 
general position on the body and the same number of parts as do 
your own (upper arm, forearm, and hand, thigh, shank, and foot, 
the latter much longer relatively than your own) . Note that while 
the frog's hand has four fingers, the foot has five toes, the latter 
connected by a web. In swimming most of the frog's energy is 
used in the powerful backward push of the hind legs, which in a 
resting position are held doubled up close to the body. On land, 
locomotion may be by hopping or crawling. 

Adaptations for life in the water are numerous. The ovoid 
body, the head merging into the trunk, the slimy covering (pro- 
vided by mucus cells in the skin), and the powerful legs with webbed 
feet, are all evidences of the life which the frog leads. 



Sense Organs. — The frog is well provided with sense organs. 
The e3^es are large, globular, and placed at the sides of the head. 
Sometimes you can see a delicate fold, or third eyelid, called the 
nic'titating membrane, drawn over each eye. A frog's vision is 
much keener than that of a fish ; it is probably best for moving 
objects at the distance of a few feet. The external ear {tym'- 
panum) is located just behind the eye on the side of the body. 
Frogs hear sounds and distinguish various calls 
of their own kind, as is proved by the fact 
that frogs recognize the warning notes of their 
mates when any one is approaching. The in- 
ner ear has to do with balancing the body, 
as it has in fishes and other vertebrates. Taste 
and smell are probably not strong sensations 
in frogs or toads. They bite at moving objects 
of almost any kind when hungry. The long 
flexible tongue, which is fastened at the front, 
is used to catch insects. Experience has taught 
these animals that moving things, insects, 
worms, and the like, make good food. These 
they swallow whole, the tiny teeth being used 
to hold the food. Touch is a well-developed 
sense. The skin is provided with many tiny 
blood vessels, and in winter, while the frogs 
are dormant at the bottom of the ponds, it 
serves as the only organ of respiration. 
Organs and Functions of the Higher Animals. — The same 
general functions performed by a single cell are performed by a 
many-celled animal. But in the many-celled animals the various 
functions of the single cell are taken up by the organs. In such 
a complex organism as the frog or man, the organs and the func- 
tions they perform may be briefly given as follows : — 

(1) The organs of protection, such as the skin and the outside 
skeleton seen in a turtle. 

(2) The organs of /oo(i ^a/cmg.' the mouth and parts which place 
food in the mouth. 

(3) The organs of digestion : the food tube and the collections of 
cells which form the glands connected with it. The enzymes in 

This diagram shows 
how the frog uses its 
tongue to catch in- 


the iiuids secreted by the glands change the foods from a solid form 
(usually insoluble) to that of a fluid. Such fluids may then pass, 
by diffusion, through the walls of the food tube into the blood. 

(4) The organs of circulation: the tubes through which the 
blood, bearing its organic foods and oxygen, reaches the tissues of 
the body. In simple animals, as the hydra, no such organs are 
needed, the fluid food passing from cell 
to cell by diffusion. 

(5) The organs of respiration: gills or 
lungs, the organs in which the blood re- 
ceives oxygen and gives up carbon di- 
oxide. The outer layer of the body serves 
this purpose in very simple animals. 

(6) The organs of excretion: such as 
the kidneys and skin, which pass off 
nitrogenous and other waste matters from 
the body. 

(7) The organs of locomotion : muscles 
and their attachments and connectives ; 
namely, tendons, lig'aments, and bones. 

(8) The organs of nervous control : the 
central nervous system, which has con- 
trol of coordinated movement. There are 
scattered nerve cells in low forms of life ; 
such cells are collected into groups and con- 
nected with each other in higher animals. 

(9) The organs of sense : collections of 
cells having to do with the reception and 
transmission of sight, hearing, smell, 
taste, touch, pressure, and temperature 

(10) The organs of reproduction: the 
sperm-forming and egg-forming organs. 

The Human Body a Machine. — In all animals, and the hu- 
man organism is no exception, the body has been likened to a 
machine in that it turns over the latent or potential energy stored 
up in food into kinetic energy (mechanical work and heat), which 
is manifested when we perform work. One great difference exists 

The human body seen from 
the side in longitudinal sec- 
tion, tr, trachea ; g, lungs ; 
d, diaphragm ; n, pancreas ; 
s, spleen ; k, kidney ; ap, ap- 


between an engine and the human body. The engine uses fuel 
unUke the substance out of which it is made. The human body, 
on the other hand, uses for fuel the same substances as those out 
of which it is formed ; it may, indeed, use part of its own substance 
for fuel. The human organism must do more than purely mechan- 
ical work. It must be so delicately adjusted to its surroundings 
that it will react promptly and efficiently to stimuli from 
without ; it must be able to utilize its fuel (food) in the most 
economical manner ; it must be fitted with machinery for trans- 
forming the energy received from food into various kinds of work ; 
it must properly provide the machine with oxygen so that the 
fuel will be oxidized; and the products of oxidation must be 
carried away, as well as other waste materials which might harm 
the effectiveness of the machine. Most important of all, the 
human machine must be able to repair itseK. 

The Value of Understanding our Bodies. — Since the purpose 
of this book is to help prepare young people to become good citi- 
zens, this chapter is of special importance. No boy or girl can 
go into the big game of life with an insufficient knowledge of the 
human machine and expect to be a helpful member of society. 
Neglect or lack of care of our bodies may defeat some of our life's 
fondest ambitions. The efficient citizen usually is the healthy 

The Skin. — Covering the body is the protective structure 
called the skin. Under the epidermis, a layer of dead cells, there 
are deficate sense organs, lying in the dermis or true skin, which 
give us sensations of touch, pressure, and temperature. The skin 
aids also in passing wastes out of the body by means of sweat 
glands, and it plays an important part in equalizing the tempera- 
ture of the body. Hairs are present on most parts of the body, 
growing from tiny outgrowths of the deep living skin, the true 
skin. They are kept soft by means of oil secreted by glands at 
the base of each hair. 

The skin is first of all an organ of protection against man's 
microscopic foes, the bacteria. But a dirty skin harbors bacte- 
ria. Moreover, the skin pores, through which the sweat passes, 
are easily clogged with dirt. Frequent washing is necessary if 
we wish to keep the skin clean. Pride in one's own appearance 



forbids a dirty skin. Powder or rouge does not clean the skin ; 
it may cover up dirt. 

For those who can stand it, a cold sponge bath or shower is best, 
with a brisk rub-down afterward, since this exercises the blood ves- 
sels of the skin. Soap should be used daily on parts exposed to 
dirt, because it combines with the oil of the skin, thus aiding in 
the removal of the dirt held there. Exercise in the open air is 
important to all who desire a good complexion. To have the 
^' glow of health " one must exercise the skin as well as keep it 

Skin Infections and their Care. — We are all aware of the 
fact that sometimes a scratch or cut becomes infected; bacteria 

Spider mis. ^ 

Sense organ. 



Bhod vessel. 


Ducf- of smreaf gland 
Shaff of hair 
m\- Muscle 

-Oil gland 
Sweat gland' 

Hair follicle 

Section of human skin. 

multiply there and cause pus. Pimples are often caused by 
the infection in the oil pores of rod-shaped bacteria, while boils 
are usually caused by the infection of the hair sacs with pus-form- 
ing bacteria — the streptococci (strep -t6-k6k'sl). 

In case the skin is badl}^ broken, it is necessary to prevent the 
entrance and growth of bacteria. This may be done by washing 
the wound with weak antiseptic solutions such as 3 per cent carbolic 
acid or 3 per cent lysol, or with peroxide of hydrogen (full strength), 
or with zonite. These solutions should be applied immediately. 
A burn or scald should be covered at once with a paste of baking 
soda, with olive oil, or with a mixture of limewater and linseed oil. 
These tend to lessen the pain by keeping out the air and reducing 
the inflammation. 





Vim - 


Phalanges \ 


- Humerus 

FeMc girdle 

Bones and Muscles. — The body is built around a framework of 
bone^. These bones, which are bound together by tough ligaments, 
fall naturally into two great groups : the bones of the body proper, 
namely, the vertebral column, ribs^ breast bone, and skull, which 

form the ax'ial skeleton; and 
the bones of the appendages, 
the framework of the arms and 
legs, which, together with the 
bones attaching them to the 
axial skeleton, form the appen- 
dic'ular skeleton. 

To the bones are attached 
the muscles of the body. 
]\Iovement is accomphshed by 
the contraction of muscles, 
which are attached so as to 
cause the bones to act as levers. 
Muscles usualh^ act in paks : 
one muscle extends while the 
other flexes or bends. Bones 
also protect the nervous sys- 
tem and other delicate organs. 
The bony cra'nium, inclosing 
the brain, is an example of suck 
protection. The internal skele- 
ton also helps to give form and 
rigidity to the bod3^ 

Hygiene of Muscles and 
Bones. — Young people espe- 
cially need to know how to 
prevent certain defects which are largely the result of bad 
habits of posture. Posture is a position of equilibrium of the 
body which can be maintained for some time, such as standing or 
sitting. Standing erect is a good habit, round shoulders are an 
indication of a bad habit. The habit of keeping a wrong position 
of bones and muscles, once formed, is very hard to correct. 

Round shoulders are most common among people whose occu- 
pation causes them to stoop, A wrong position at one's desk 

Skeleton of a man 






is among the causes. Exercises which strengthen the back muscles 
are helpful in forming the habit of erect carriage. 

ffumerus- — 

Radius and uind, ^ 

bones of the forearm 

Diagram showing action of biceps muscle. 

The muscle cells 2 
have (onfracfed 

Muscles work in pairs, as A and B. 

Slight curvature of the spine either backward or forward is 
helped most by exercises which tend to straighten the body, such 
as stretching up with the hands above the head. Lateral curvature 
of the spine, too often caused 
by a "hunched-up" position 
at the school desk, may also 
be corrected by exercises which 
tend to lengthen the spinal 

One of the most frequent 
types of postural defect, found 
during the World War, is flat- 
foot. Tight shoes, high heels, 
and '' toeing out " all play a 
part in this defect. A severe 
case produces strain known as 
a '' broken arch," and this 
condition may produce severe 
pain or even nervous disorders. 
An orthopedic specialist should 
be consulted in such cases. 

It is the duty of every girl 
and boy to have good posture 
and erect carriage, not only 

because of the better state of Bad posture. Good posture. 


health which comes with it, but also because self-respect demands 
that we make the best of the gifts that nature has given us. An 
erect head, straight shoulders, and elastic carriage go far toward 
making their owner both liked and respected. 

Other Body Structures. — In spaces between the muscles are 
found various other structures — blood vessels, which carry blood 
to and from the great pumping station, the heart; connective 
tissue, which holds groups of muscle or other cells together ; fat 
cells, scattered in various parts of the body ; various gland cells, 
which manufacture enzymes ; and the cells of the nervous system, 
which aid in directing the various parts of the body. 

Body Cavity. — Within the cover of skin, bone, and muscle 
is a cavity filled with various organs. A thin wall of muscle 
called the diaphragm (df d-fram) divides the body cavity into 
two unequal spaces. In the upper space are found the heart and 
lungs; in the lower, the digestive tract with its glands, the liver, 
the kidneys, and other structures (see page 111). 

Digestion and Excretion. — The mouth cavity leads into a 
food tube in which undigested food is placed and from which di- 
gested or liquid food is absorbed into the blood to be carried to 
the cells of the various organs which do the work. Emptying 
into this food tube are various groups of gland cells, which pour 
digestive fluids over the solid foods, thus aiding in changing 
them to a soluble form. Solid wastes are passed out through 
the posterior end of the food tube, while liquid wastes are 
eventually excreted by means of the skin and of organs called 

The Nervous System. — This complex machine is much more 
than a mechanical engine. It is self-directed. All its functions 
are either directly or indirectly under its control. Not only are 
animals able to receive outside stimuli through certain parts called 
sense organs, but they react to them, and there is internal coordi- 
nation and control as well. The complicated machine does its 
work automatically; the heart beats, the glands secrete, the 
chest rises and falls without any conscious direction on our part. 
The nervous system gives sensation, it gives internal control 
and coordination. In man it does more. It also gives him con- 
trol over his conscious activities. He is able to make a selection 



or choice of his daily acts. As such he is a " thinking " animal 
and has become master of the earth. 

Summary. — As we progress from simple forms of animal Ufe 
toward more complex forms, we note an increasing complexity in 
the division of labor. But no matter how simple or how complex 
the animal, all have certain functions, and in the many-celled ani- 
mals we find definite organs of sensation, protection, locomotion, 
food-taking, digestion, circulation, respiration, excretion, nervous 
control, and reproduction. In the human body these organs are 
most highly developed. 

One of the organs of protection, the skin, must be cared for 
properly if we wish to keep it healthy. Skin infections sometimes 
prove very serious. The hygiene of muscles, bones, and posture 
is of importance, especially to growing children. 

Problem Questions 

1. Give different examples of division of labor from your own experience. 
Is there division of labor in society? 

2. In what respects is a frog like man in structure? 

3. What functions are common to all animals? To many-celled ani- 
mals ? To animals and plants ? 

4. In what respects is the body like a machine? 

5. What is the proper first-aid treatment for an infected wound ? Why? 

6. Why is flatfoot an important defect? 

7. Of what use to man is the nervous system ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Davison, The Human Body and Health. American Book Company. 

Holmes, Biology of the Frog. The Macmillan Company. 

Hough and Sedgwick, The Human Mechanism. Ginn and Company. 

Howell, Physiology. W. B. Saunders Company. 

Martin, The Human Body, Advanced Course. Henry Holt and Company, 

Sharp, Foundation of Health. Lea and Febiger. 

Stiles, Human Physiology. W, B. Saunders Company. 

WilUams, Text-Book of Anatomy and Physiology. W. B. Saunders Company. 



Problems: A study of foods to determine: 
(a) Their nutritive value, 
(h) The value of vitamins. 

(c) The relation of work, environment, age, sex, and digestibility 
of foods to diet. 

(d) The relative cheapness of different foods. 

(e) The daily calorie requirement. 

Laboratory Suggestions 

Laboratory exercise. Composition of common foods. The series of food 
charts suppHed by the United States Department of Agriculture makes an 
excellent basis for a laboratory exercise to determine common foods rich in 
(a) water, (5) starch, (c) sugar, (d) fats or oils, (e) protein, (f) salts, {g) refuse. 
New charts on vitamins made by American Medical Association. 

Demonstration. Method of using bomb calorimeter. 

Laboratory and home exercise. To determine the best balanced dietary for 
yourself (using standard of Atwater, Chittenden, or Voit) as determined by the 
use of the 100-calorie portion. 

Why we need Food. — A locomotive engine takes coal, water, 
and oxygen from its environment. A living plant or animal gets 
food, water, and oxygen from its environment.^ Both the living 
and the non-living machine do the same thing with this fuel and 
part of this food. They oxidize it and make use of the energy 
thus released. But the living organism in addition may use food 
to repair parts that have broken down, or even to build new 
parts. Thus food may he defined as something that can he used by 
the body of a plant or animal to release energy, or that forms mate- 
rial for the growth or repair of the body of a plant or animal. The 

^ Animals and some plants get organic food from their environment ; but green 
plants, as we have seen, make their organic food from materials which they get 
from their environment. 








Composition of milk. 
Why is milk consid- 
ered a good food ? 

millions of cells of which the body is composed must be given 
material which will form more protoplasm ; also food material 
which can be oxidized to release energy when muscle cells move, 
or gland cells secrete, or brain cells think. 

Nutrients. — Certain nutrient materials form the basis of food 
of both plants and animals. These, as already stated (page 53), 
include proteins (such as lean meat, eggs, the 
gluten of bread) , carbohydrates (starches, sugars, 
gums, etc.), fats and oils (both animal and vege- 
table), mineral matter, and water. Not many 
years ago biologists thought that if the body 
was supplied with sufficient quantities of water 
and of proteins, fats or oils, and carbohydrates, 
it would grow and do its work well. But re- 
cent scientific work on dietaries shows that 
other factors also must be considered. Feed- 
ing experiments with rats and other animals, 
and with people, have shown that vitamins and 
certain minerals are necessary. 

The Fuel Value of Food. — In various experiments it has been 
agreed that the energy stored in foods as a source of heat should be 
stated in heat units called calories. A calorie is the amount of heat 
required to raise the temperature of one kilogram of water one degree 
Centigrade.^ This is about equivalent to raising the temperature 
of one pound of water four degrees Fahrenheit. The fuel value 
of different foods may be computed in a definite manner. This is 
done by burning a given portion of each food (one gram) in the ap- 
paratus known as a calorim' eter . By this means may be determined 
the number of degrees the temperature of a given amount of water is 
raised during the process of burning. It has thus been found that a 
gram of fat will liberate 9.3 calories of heat, while a gram of starch 
or sugar liberates only about 4 calories. The burning value of 
fat is, therefore, over twice that of carbohydrates. In a similar 

^ The calorie thus defined, the one used in food experiments, is sometimes spelled 
with capital C and is called the " large calorie " to distinguish it from the small calorie 
which is used for delicate physical measurements. The small calorie is equal to one 
thousandth of the large calorie. For very precise measurements the small calorie 
is defined as the amount of heat required to raise the temperature of one gram of 
water " from 15° C. to 16° C," instead of merely " one degree Centigrade." 


manner protein has been shown to have about the same fuel value 
as carbohydrates, i.e. 4 calories to a gram. 

Fats and oils have the highest energy value of all foods. But 
because of their rather indigestible qualities and because one soon 
tires of an excessive amount of fat in one's dietary, carbohydrates 
are more used to release energ}^ Cereals, bread, potatoes, and 
other starchy vegetables should, for this reason, be a part of our 
daily dietary. 

Tissue Building and Repair of Waste. — But it is not sufficient 
for man to '' count his calories." We are made of living matter, 
protoplasm. Living cells may waste away, and need to be 
repaired or replaced. New cells must be formed. We grow in 
weight up to early manhood or womanhood, and after that the body 
weight may rise or fall, depending on our health or constitution. 
Evidently, then, the tissues use food for building purposes. 

We have already seen that carbohydrates, fats, and proteins 
all contain the elements carbon, oxj^gen, and hydrogen, and that 
proteins alone contain the element nitrogen. We have learned 
also that this wonderful substance, protoplasm, is either a very 
complex compound or a mixture composed of carbon, hydrogen, 
ox^^gen, nitrogen, and ten or more other chemical elements which 
are found in soil or rock.^ Therefore if living matter is to grow, 
it must have the proper elements for building. Such of these ele- 
ments as are not present in carbohydrates and fats are found in 
proteins. Proteins, although they may be oxidized to release 
energy, must be used to give the body its nitrogen from which, in 
part, living protoplasm is manufactured. 

Not all Proteins are Good Tissue Builders. — Recent feeding 
experiments have shown that not all proteins are capable of build- 
ing tissues. It has been found that the complex chemical sub- 
stance called protein may be broken by the chemist into simpler 
proteins caUed am'ino-acids. Some of these amino-acids are useful 
in tissue building, and others are not.^ If two rats are fed on diets 

^ The elements in protoplasm obtained by chemical analysis are carbon, hydro- 
gen, oxygen, nitrogen, sulphur, phosphorus, fluorine, chlorine, silica, iron, potas- 
sium, sodium, calcium, magnesium, and others. 

2 It is found that some proteins will form new tissue, others may be used in the 
body only to maintain body weight, and still others contain no amino-acids capable 
of being used in tissue building. 


containing different amino-acids, one may thrive, while the other 
wastes away and dies. For example, gelatin is a very poor type 
of protein, because it does not contain the necessary amino-acids 
for tissue building or tissue repair. On the other hand, the pro- 
teins of milk contain the amino-acids necessary for growth. It is 
estimated that there are about twenty of these amino-acids, and 
that all of those essential for growth are found in milk, eggs, wheat 
and a few other grains, and nuts. So it happens that most of us, 
without knowing why, have used for food the proteins containing 
the essential amino-acids. 

The Value of Mineral Substances in our Dietary. — It has long 
been known that water and the various mineral salts it contains 
are essential to life. The human body, by weight, is about two 
thirds water. About 90 per cent of the blood is water. Water is 
absolutely essential in passing off the waste of the body. When 
we drink water, we take with it some of the inorganic salts used by 
the body in the making of bone and in the formation of protoplasm. 
Sodium chloride (table salt), an important part of the blood, is 
taken in also as a flavoring upon our meats and vegetables. Phos- 
phate of lime and potash are important factors in the formation of 

But it is only recently that scientists have learned how impor- 
tant a part is played by minute quantities of certain mineral sub- 
stances. For example, the clotting of our blood, without which 
we should bleed to death from the smallest cut, appears to depend 
on the presence of calcium in the blood. 

Some other salts, compounds of magnesium, potassium, and 
phosphorus, aid the body in many of its most important functions. 
The beating of the heart, the contraction of muscles, and the 
ability of the nerves to do their work appear to depend on the pres- 
ence of minute quantities of these salts in the body. Thus they 
act as regulators of bodily activity. 

Vitamins and their Uses. — Far more wonderful regulating sub- 
stances are the vitamins. While little is known of their chemical 
composition, a good deal has recently been learned of what they 
do, or, rather, of what their absence will cause. These mysterious 
health-regulating substances are known as Vitamins A, B, C ; also 
the recently-discovered Vitamins D and E. A glance at the table 



















Lean muscle 





• •• 

• • 

Pork, lean 






• ••• 

•■ fat 


Potatoes, white 


• •• 

• •• 


Beans, kidney 



•' navy 











• ••• 



• •.. 





• •• 





Peas, fresh 




• • 




• ••• 

Fish, roe 


• • 






• • 

• •• 



• • 



• •• 



• • 


Brazil nuts 

• •• 




• •• 


• •• 



• •• 







Hickory nuts 


• •• 


Cod Liver Oil 

• •••• 



• •• 




• •• 

Corn Oil 


Walnuts, English 

• •• 

Margarine, oleo 


■ ' black 


Mutton fat 



Beef fat 


Milk, whole 







i • 1 

" skim 


• •a 





■' condensed 


• •• 



" sweetened 

• •• 

• •a 




• • 


■■ evaporated 






• • 

■■ powdered 


• •• 


• •• 


Lemon juice 

• •• 

Cheese, whole milk 





• • 

• •• 



• • 



Orange juice 

• • 

• •• 

• •••• 

Molasses, beet 


Tomatoes, raw 


• •• 

• •••• 

" sorghum 




• •• 

• •••• 




• • 






Eggs, yolk 




Wheat, whole 


• ••• 



" germ 


• •••• 



" bran 



Green grass 

• ••• 


Corn, white 



• •a. 


•• yellow 







• •• 




... 1 


Rice, bran 

• •••* 



• •a 


• Indicates a small amount 

•• a fair amount 

••• a relatively large amount 
...• abundance 
••..eexceptionally large amount 

Table of vitamins, compiled from the work of the Bureau of Chemistry, Wash- 
ington, D. C. 


shows that Vitamm A, sckible in fats, is abundantly found in milk, 
egg yolk, and butter, and in lesser amounts in certain vegetables. 
Vitamin B, soluble in water, is found in the outer layers of many 
cereals, and in eggs, fresh yeast, and many other fresh foods. 
Vitamin C is found in many fresh vegetables and fruits. Vitamin 
D is fat soluble and is found in cod liver oil, milk, and coconuts. 
Vitamin E is found in wheat and other cereals. Vitamins appear 
to be largely of plant origin and in many cases are destroyed or at 
least their value to the body is lessened by heat, although some 
stand high temperatures, as in canned tomatoes or boiled potatoes. 
So much for what they are. Now what do they do? It has 
been known for a good many years that explorers deprived of fresh 

Pigeon that has animal beriberi. Same pigeon three hours after eating 

Vitamin B. 

A pigeon fed on polished rice develops the disease known as animal beriberi 
(polyneuritis) ; when fed material containing Vitamin B it is soon cured. This 
experiment was first described by Casimir Funk, who gave the name " vitamines " 
to these substances. 

food suffer from the disease called scurvy. This deficiency disease 
has been found to be caused by a lack of Vitamin C. Experi- 
ments carried on in the Japanese navy about 1890 showed that 
beriberi, a serious menace to health among oriental peoples, is 
caused by a lack of nutrients not present in the rice and fish which 
form the major part of their dietary. Later experiments showed 
that the lack of Vitamin B causes beriberi. An eye disease called 
xeropthalmia is caused by a lack of Vitamin A. Recent experiments 
seem to indicate that rickets, a disease of children, '' characterized 
by impaired nutrition and alterations in the growing bones," is 
caused by a lack of Vitamin D. Lack of Vitamin E appears to 
cause sterility in animals. 


What we should eat. — It is evident from what has abeady 
been learned that our daily dietary should include all of the organic 
nutrients, in proper proportions. We must eat to work as well as 
to grow or to repair our bodies. Our food must contain plenty 
of water, and we must be sure that we have a supply of certain 
mineral salts. And perhaps most important of all, we must have 
a supply of vitamins, in order that nutrition and growth may 
take place. 

Common Foods contain the Nutrients. — We have already 
found in our study that various plant foods are rich in different 
nutrients. Carbohydrates form the chief nutrient in the foods we 
call cereals, bread, cake, fleshy fruits, sugars, jellies, and the like. 
Fats and oils are most largely found in nuts and some grains. 
Proteins are abundant, as we should expect, in those plants which 
are richly supplied with nitrogen : peas and beans, and in grains 
and nuts. Animal foods, however, are our chief supply of protein. 
White of egg and lean meat are almost pure protein and water. 
Animal foods also supply much fat ; for example, butter, lard, and 
the fat in meats. 

Water. — Water is, as we have seen, a valuable part of food. 
It makes up a very high percentage of fresh fruits and vegetables ; 
it is also present in large proportion in milk and eggs, is less abun- 
dant in meats, and is lowest in dried foods and nuts. The amount 
of water in a given food is often a decided factor in its cost, as can 
easily be seen by reference to the tables on pages 125 and 131. 

Refuse. — Some foods bought in the market may contain a 
certain unusable portion. This we call refuse. Examples of 
refuse are bones in meat, shells of eggs or of shellfish, the covering 
of plant ceUs which form the skins of potatoes, and other vegetables. 
Part of this refuse, called roughage, is important in our dietary as 
it stimulates the muscles of the bowels to move and thus aids in 
preventing constipation. The amount of refuse present also 
plays an important part in the values of foods. The table ^ on 
page 125 gives the percentages of organic nutrients, water, and 
refuse present in some common foods. Similar information is 
given by the diagrams on pages 126, 127, and 128. 

1 W. O. Atwater, Principles of Nutrition and Nutritive Value of Food, U. S. De- 
partment of Agriculture, 1902. 



Table of food values. Determine the percentage of water in codfish, loin of beef, 
milk, potatoes. Percentage of refuse in leg of mutton, codfish, eggs, and potatoes. 
What is the refuse in each case? Find three foods containing a high percentage of 
protein ; of fat ; of carbohydrate. Find some food in which the proportions of 
protein, fat, and carbohydrate are combined in a good proportion. 


I S BfpVtrneot of Aflrieultuic Prcparca By 

OH.ce 0' t»ocrimenl Stlt.onj C. F. LAN6W0RTMY 



er.58.9 i^' "W3ter:l?.6 

720 Ufa pouno 1 560 t.ioxis pi « oou«o 







U.S. Oepdfiment of Agrlcult 

Offict 0( i.pennnnl Stjlio 



IS Ash vvatti 


_VVater:35.i Water: 38 
Protein- 9 2 Protein-.9.7 

Deoi'lme"! 0' Agncutlurt PfCpdrefl b, 

t. ol £.pf'rm,„, Slil.o-W C. F. LAN6W0BTBY 

A. C. Tfue: D-'ector Eipct la Charge of Nutr.fion Invest 


I. S. Deparimem oi Agriculture 

Office of txperimenT Stations 

A. C. True; Director 

Prepared by 


^m Mm f^?^ ^^ ^M ^ """ ^" 

P.otein ("at Carbofijdcatcs Ash 


1000 Calone; 

Carbohydrates 100.0 

Carbohydrates 69 3 


rCarbohydrates:96 5 

1300 cALomes 

MAPLE SUGAR 1745 calories 

-Water: 16.3 Water: 18.2, 

Carbo- Carbo- 

hydrates:82.8 hydrates-.8l.2 

Foods of plant origin. Select five foods containing a high percentage of protein, 
five with a high percentage of carbohydrates, five with a high percentage of water. Do 
V 'g'-table foods contain much fat? VHiich of the above-mentioned foods have the 
highest burning value? Which contain vitamins? 




I E<pe'irr,<ni Srstio 

Coert in Charge ol Nulrilion li 


r?rn mm ^m tsm, p-^vai.e 

^^■l^gSq n Equa 
l^" lOOOCdlorij 


.Bj.lmcot Of Aqriculure Repsrtd b, 

e of I ipenmenl Stations C. F. UNGWORTHY 

A. C. True: Oiieuor Expert ,o Chjrge of Nutrition Invcstigall 


^S. Oepjrtment of Agriculture Prepared b) 

Ollrce of itptnment Stations C,F. LAMGW0R7HY 

A.C. True: Director Enpert fn Charge of Nutrition lni/esti( 


4080 UL01IE3 P(» 

Foods largely of animal origin. Compare with the previous chart with reference 
to amount of protein, carbohydrate, and fat in foods. Compare the burning value of 
plant and animal foods. Compare the relative percentage of water in both kinds 
of foods. Are vitamins as abundant as in plant foods? 


Prepared by 


Ejtperl in Charge of Nutrition Investigationa 


^^ dU MM ^M ^M WMvZ] 

P-ottin fat Carbohydrate! Ash Water ^Bl'mOO 

Food Accessories. — Most of us are aware that flavoring ma- 
terials such as pepper, mustard, and other condiments are not 
true foods. Meats, fruits, and vegetables have flavors of their 
own, but the cook " brings them out " by a skillful use of salt, 
spices, and other food accessories. While flavoring extracts and 
meat and vegetable flavors (called extractives) do not have food 
value, yet they are of great use in stimulating the appetite. On 
the other hand, excessive use of extractives and spices is said to 
have a serious effect on blood pressure and on the kidneys. Tea 

and coffee are often used for 
their stimulating effect as well 
as for their flavor. 

The Relation of Work to Diet. 
— It has been shown experi- 
mentally that a man doing hard, 
muscular work needs more food 
than a person doing light work. 
The mere exercise gives the in- 
dividual a hearty appetite; he 
eats more and needs more of 
all kinds of food than a man or 
boy doing light work. Espe- 
cially is it true that the person 
of sedentary habits, who does 
brain work, should be careful 
to eat less food and food that 
will digest easily. His protein 
food should also be reduced. 



^Water 91.1 

-.3 Fat: 18.5-^ 
Ash .-OS 


The composition of milk. 

Rich or hearty foods may be left for the man who is doing hard 
manual labor out of doors. 

The Relation of Environment to Diet. — We are all aware of the 
fact that the body seems to crave more food in winter than in 
summer. The temperature of the body is maintained at 98.6° in 
winter as in summer, but much more heat is lost from the body in 
cold weather. Hence we need more heat-releasing food in winter 
than in summer. We may use carbohydrates for this purpose, as 
they are economical and easily digested. The inhabitants of cold 
countries get their heat-releasing foods largely from fats. In 



tropical countries and in hot weather a considerable amount of 
fresh fruit should be used in the dietary. 

The Relation of Body Size and Age to Diet. — A large person, of 
course, needs more food than a small one. Why? Age is a factor 
in determining not only the kind but also the amount of food to 
be used. Young children require a large proportion of protein in 
their diet in order to grow. They are also more active than older 
persons and so use a large amount of food as fuel in proportion to 
their weight. The body constantly increases in weight until 
young manhood or womanhood, and then its weight remains 
nearty stationary, varying with health or illness. It is evident that 
food in adults simply repairs the waste of cells and releases energy. 
Elderly people need much less protein than do younger persons. 

The Relation of Sex to Diet. — As a rule, boys need more food 
than girls, and men than women, 
the more active muscular life of 

This seems to be due, first, to 

the man, and, secondly, to a 
layer of fatty tissue directly 
under the skin of the woman, 
which acts as an insulating 
layer against loss of heat 
from the body. Larger bodies, 
because of greater surface, give 
off more heat than smaller ones. 
Men are usually larger than are 
women, — another reason why 
they require more food. 

The Relation of Digestibility 
to Diet. — Animal foods in gen- 
eral may be said to be more 
completely digested within the 
body than plant foods. This is 
largely due to the fact that plant cells have woody walls that the 
digestive juices cannot dissolve. Heat causes the starch grains to 
swell and break these woody walls, and that is the reason for the 
thorough cooking of vegetable foods. Cereals and legumes are less 
digestible foods than are milk and eggs. Plant proteins in general 
do not have as many useful amino-acids as do animal proteins. 




In the potato, the starch grains are 
formed inside of the cell. 


The agreement or disagreement of food with an individual is 
largely a personal matter. Jack Spratt, for example, cannot eat 
raw tomatoes without suffering from indigestion, while Mrs. Spratt 
can digest tomatoes but not strawberries. Each individual should 
learn early in life the foods that disagree with him and leave such 
foods out of his dietary. For " what is one man's meat may be 
another man's poison." 

The Relation of Appetite to Diet. — Every one likes some things 
to eat better than others. It is certain that foods which are en- 
joyed cause a flow of digestive juices, not only in the mouth but 
also in the stomach. The sight, odor, and taste of food we Uke 
actually aids in digestion. '' Digestion waits on appetite." If we 
use common sense in the selection of foods, taking care to avoid 
foods that we cannot easily digest, we shall find that the appetite 
is often a guide in the selection of foods. 

The Relation of Cost of Food to Diet. — It is a mistaken notion 
that the best foods are always the most expensive. A study of 
the tables on pages 125 and 122 will show us that fuel and tissue- 
building materials as well as vitamins are present in foods from 
vegetable sources, as well as in those from animal sources; and 
the vegetable foods are usually cheaper. The American people 
are far less economical in their purchase of food than most other 
nations. A comparison of the daily diets of persons in various 
occupations in this and other countries shows that as a rule we eat 
more than is necessary to supply materials for fuel and repair. 
Another waste of money by Americans is in the false notion that 
a large proportion of the daily dietary should be meat. Many 
people thiak that the most expensive cuts of meat are the most 
nutritious. The falsity of this idea may be seen by a careful 
study of the table on page 131. 

The Nutritive Ratio. — Inasmuch as all living substance con- 
tains nitrogen, it is evident that protein food must form a part of 
the dietary ; but protein alone is not a safe choice. If more pro- 
tein is eaten than the body requires, then immediately the liver 
and kidneys have to work overtime to get rid of the excess of 
protein which forms a poisonous waste harmful to the body. We 
must take foods that will give us, as nearly as possible, the propor- 
tion of the different chemical elements as they are contained in 



Table showing the cost of various foods. Using this table, make up an economical 
dietary for one day, three meals, for a man doing moderate work. Give reasons 
for the amount of food used and for your choice of foods. Make up another dietary 
in the same manner, using expensive foods. What is the difference in your bill for 
the day? By reference to the table on page 122, tell what additional foods, if any, 
are desirable to supply all the vitamins. 


protoplasm, as well as an amount necessary to supply energy to 
the body. It has been found, as a result of studies by Atwater 
and others, that a man who does muscular work requires nearly 
one quarter of a pound of protein, the same amount of fat, and 
a little less than one pound of carbohydrate to pro\dde for the 
growth, waste, and repan of the body and the energy used up in 
one day. The proportion of protein in the diet is called the nutri- 
iive ratio. 

The Daily Calorie Requirement. — Put m another way, At- 
water says that for every 100 calories furnished by the food, 14 
should be from protein, 32 from fat, and 54 from carbohydrate. 
Professor Chittenden of Yale University, another food expert, 
thinks we need proteins, fats, and carbohydrates in about the pro- 
portion of 1 to 3 to 6, thus differing from Atwater in giving less 
protein in proportion. For every 100 calories furnished by the 
food, 10 should be from protein, 30 from fat, 60 from carbohydrate. 
A German named Voit gives as ideal 25 calories from proteins, 20 
from fat, and 55 from carbohydrate, out of every 100 calories ; this 
is nearer our actual daily ration. In addition, an ounce of salt 
and nearly one hundred ounces of water are used in a day. 

A Mixed Diet Best. — Knowing the proportion of the different 
nutrients required by man, and the foods containing vitamins, 
it will be an easy matter to determine from the foregoing 
tables and charts the best foods for use in a mixed diet. Meats 
contain so much nitrogen that they should be eaten with other 
foods. In milk, the proportion of proteins, carbohydi'at^s, and 
fats is nearly right to make protoplasm, a considerable amount 
of mineral matter also being present. For these reasons, milk is 
extensively used as a food for children, as it combines food material 
for the forming of protoplasm with mineral matter for the building 
of bone, and it also contains the vitamins. Some vegetables (for 
example, peas and beans) contain a large amount of nitrogenous 
material, but not all the amino-acids needed for growth seem to be 
present. A purely vegetable diet contains much waste material, 
such as the cellulose forming the waUs of plant cells, which is in- 

Basal Metabolism. — The life activities of a plant or animal, 
which include all the chemical processes that go on in the body, 



are known collectively as the meiabol'ic processes (Gr. metaholos, 
changeable). These changes release heat as a by-product and 
this heat can be measured in calories. The heat-producing activ- 
ity of the body protoplasm during sleep or rest represents the en- 
ergy which is essential for carrying on the vital processes and 
is known as basal metab'olism. It is represented in a man of 
average weight (about 150 pounds) by about 65 calories an hour. 
Normal Heat Output. — The following table gives the result of 
some experiments made to determine the hourly and daily expen- 
diture of energy of the average normal grown person when asleep 
and awake, at work or at rest : — 

AvEEAGE Normal Output of Heat from the Body 

Conditions of Muscular Activity 

PER Hour 

Man at rest, sleeping (basal metabolism) . , 

Man at rest, awake, sitting up 

Man at light muscular exercise 

Man at moderately active muscular exercise 

Man at severe muscular exercise 

Man at very severe muscular exercise . . . 

65 calories 
100 calories 
170 calories 
290 calories 
450 calories 
600 calories 

It is very simple to use such a table in calculating the number 
of calories which are spent in twenty-four hours under different 
bodily conditions. For example, suppose the case of a clerk or 
school teacher leading a relatively inactive life, who 

sleeps for 9 hours X 65 calories = 585 

works at desk 9 hours X 100 calories = 900 

reads, writes, or studies 4 hours . . X 100 calories = 400 
walks or does light exercise 2 hours . X 170 calories = 340 


This comes out, as we see, very close to example 6 of the table 
on page 134.^ 

, Daily Fuel Needs of the Body. — It has been pointed out that 
the daily diet should differ widely according to age, occupation, 

^ The foregoing tables have been taken from the excellent pamphlet of the Cornell 
Reading Course, No. 6, Human Nutrition. 

H. NEW CIV. BIOL. — 10 


time of year, etc. The following table shows the daily fuel needs 
for several ages and occupations : — 

Daily Calorie Needs (Approximate) 

1. For child under 2 years 900 calories 

2. For child from 2-5 years 1200 calories 

3. For child from 6-9 years 1500 calories 

4. For child from 10-12 years 1800 calories 

5. For girl from 12-14 (woman, light work, also) .... 2100 calories 

6. For boy (12-14), girl (15-16), man, sedentary .... 2400 calories 

7. For boy (15-16) (man, light muscular work) 2700 calories 

8. For man, moderately active muscular work 3000 calories 

9. For farmer (busy season) 3200 to 4000 calories 

10. For ditchers, excavators, etc 4000 to 5000 calories 

11. For lumbermen, etc 5000 and more calories 

How to find whether a Diet is properly Balanced. — We already 
know approximately our daily calorie needs and about the propor- 
tion of protein, fat, and carbohydrate needed. Dr. Irving Fisher 
of Yale University has worked out a very easy method of determin- 
ing whether one is living on a proper diet. He has made up a 
number of tables, in which he has designated portions of food, 
each of which furnishes 100 calories of energy. The tables show 
the proportion of proteui, fat, and carbohydrate in each food, so 
that it is a simple matter by using such a table to estimate the pro- 
portions of the various nutrients in our dietary. We may depend 
upon having somewhere near the proper amount of each nutrient if 
we take a diet based upon either Atwater's, Chittenden's, or Voit's 
standard. One of the most interesting pieces of home work that 
you can do is to estimate your own dietary, using the tables giving 
the 100-calorie portion to see if you have a properly balanced diet. 

Food Habits. — Habits play a very important part in our life 
activities. We should not think much about our daily activities, 
for once having learned the reasons for performing certain acts, 
those acts should becom^e habits. The habit of brushing teeth 
properly, the habit of proper mastication, of the choice of the right 
kuids and proportions of food, of the avoidance of tea and coffee, 
— these and other useful acts should become automatic. Some 
health habits that are worth acquiring are : — 

(1) Have your meals at regular hours. 

(2) Take time to eat and enjoy your meals. Do not bolt your 



Table of 100-Calorie Portions — Modified from Fisher 


Oysters . . . . 
Bean soup . . . 
Cream of corn . . 
Vegetable soup 
Cod fish (fresh) . 
Salmon (canned) . 
Chicken . . . . 
Veal cutlet . . . 
Beef, corned . . 
Beef, sirloin . . 
Beef, round . . . 
Ham, lean . . . 
Lamb chops . . 
Mutton, leg . . 
Eggs, boiled . , 
Eggs, scrambled . 
Beans, baked , . 
Potatoes, mashed . 
Macaroni . . . 
Potato salad . . 
Tomatoes, sliced . 
Rolls, plain . . 
Butter . . . . 
Wheat bread . . 
Chocolate cake 
Gingerbread . . 
Custard pudding . 
Rice pudding . . 
Apple pie ... 
Cheese, American 
Crackers (soda) 
Currant jelly . . 



Milk, cond., sweet 
Oranges . . . . 
Peanuts . . . . 
Almonds, shelled . 


100 Calories 

1 doz. 

I small serving 
I ordin. serv. 
I ordin. serv. 
ordin. serv. 
small serv. 
I large serv. 
I large serv. 
I large serv. 
small serv. 
small serv. 
ordin. serv. 
I ordin. serv. 
ordin. serv. 
1 large egg 
1^ ordin. serv. 
side dish 
ordin. serv. 
I large serv. 
ordin. serv. 
4 large serv. 
1 large roll 
ordin. pat 
1 small slice 

1 ord. sq. piece 
^ ord. sq. piece 
ordin. serv. 
very small serv. 
-3- piece 

1^ cu. in. 

2 crackers 

2 heap, spoons 

3 teaspoons 
small glass 

4 teaspoons 
1 large one 

13 double ones 

Wt. in 

Oz. 100 




























Cal. Furnished 
























(3) Chew your food thoroughly before swallowing it. 

(4) Do not take an excessive amount of any one food to the 
exclusion of others. Learn to eat a balanced diet. 

(5) Learn to like foods containing vitamins. 

(6) Avoid too great a proportion of highly flavored or spiced 

(7) Avoid greasy or fried food. 

(8) Avoid foods that you know do not agree with you. 

(9) Avoid mixtures that disagree with your digestion. 

(10) Do not eat when tired. Rest a few minutes before begin- 
ning your meal. 

(11) Drink plenty of water, at least six glasses a day, preferably 
between meals. 

Summary. — The following table, modified from Atwater's 
Principles of Nutrition and Nutritive Value of Food, sums up the 
uses of the nutrients. 

All serve as fuel 
and yield energy in 
form of heat and 
muscular strength. 

Protein Forms tissue (mus- 

White of eggs (albumen), cles, tendon, and 
curd of milk (casein), lean probably fat). 
meat, gluten of wheat, etc. 

Fats Form fatty tissue. 

Fat of meat, butter, olive oil, 
oils of corn and wheat, etc. 

Carbohydrates Transformed into fat 

Sugar, starch, etc. 
Vitamins Regulative substances which prevent cer- 
tain deficiency diseases, as scurvy, beri- 
beri, rickets, xerophathalmia. 
Mineral matters (ash) .... Aid in forming bone, assist in digestion, aid 
Phosphates of lime, potash, in absorption, and in other ways help the 
soda, etc. organs to do their work. 

Water is used as a vehicle to carry nutrients, and enters into the composition 
of living matter. 

A dietary has a distinct relation to 

(a) the kind of work a person does ; 

(6) the place where he lives ; 

(c) the sex of the individual ; 

{d) the age of the individual ; 

(e) the digestibility of food ; * 

(/) the cost of food ; 

((/) the relation of appetite to food. 


A mixed diet is shown to be best and for the average person doing 
moderate work the ratio per day should be about 3 to 4 oz. of pro- 
tein to 16 oz. of carbohydrate and 4 oz. of fats. 

The fuel needs of the body have been carefully determined. The 
amount needed for a boy or girl of high school age runs from 2100 
to 2700 calories, depending on the occupation. 

Problem Questions 

1. What are vitamins? What do they do? How were the values of 
vitamins discovered? 

2. What are amino-acids ? 

3. What is a food? 

4. What is a calorie? How is it determined? 

5. What is a balanced diet? Give examples. 

6. Why are certain vegetables included in a balanced diet? 

7. What are cheap foods ? Expensive foods ? Give examples. 

8. What are the daily calorie needs and how are they determined? 

9. Give some standards for a well-balanced diet. 
10. What is a 100-calorie portion? Illustrate. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Allen, Civics and Health. Ginn and Company. 

Bulletin 13, American School of Home Economics, Chicago. 

Buls. 6 and 7, Human Nutrition. Cornell University Reading Course. 

Cohnheim, Enzymes. John Wiley and Sons. 

Davison, The Human Body and Health. American Book Company. 

Ellis and Macleod. Vital Factors of Foods, Vitamins and Nutrition. D. Van 

Nostrand Company. 
Funk, The Vitamines. Williams and Wilkins. 
Harrow, Vitamines. E. P. Dutton and Company. 
Hough and Sedgwick, The Human Mechanism. Ginn and Company. 
Jordan, The Principles of Human Nutrition. The Macmillan Company. 
Lusk, Science of Nutrition. W. B. Saunders Company. 
McCoUum and Simmonds, The Newer Knowledge of Nutrition. The MacmUlan 

Norton, Foods and Dietetics. American School of Home Economics. 
Sherman, Chemistry of Food and Nutrition. The Macmillan Company. 
Stiles, Nutritional Physiology. W. B. Saunders Company. 
Farmers' Bulletins 23, 34, 42, 85, 93, 121, 128, 132, 142, 182, 249, 256, 295, 

298, 717, 817, 824, 975, 1313, 1383. 




Problems : To learn what adulterations are and how to avoid them 
To learn the effect of stimulants and of narcotics in the body. 
To find out whether alcohol is a food or a poison. 
To learn the dangers connected with patent medicines and drugs. 

Laboratory Suggestions 

Laboratory demonstration. Some adulterations detected under the micro- 

Exercise. Some adulterations detected with chemicals. 

Demonstration. The effect of alcohol on white of egg. 

Demonstration. The effect of nicotine on living protozoa or living fish. 

Demonstration. Some patent medicines and their dangers. Use charts 
prepared by American Medical Association. 

Pure Food Law. — In 1906 Congress passed a Pure Food and 
Drug Act that defined adulteration and to some extent remedied 
conditions in the preparation of foods that enter into interstate 
commerce. Before the passage of this act, about half of nearly 
2000 samples of food examined were shown to be adulterated. 
To-day both adulteration and misbranding of food are forbidden 
under severe penalties. 

What is Adulteration ? — The addition of some cheaper sub- 
stance to a food, the subtraction of some valuable substance from 
a food, or the addition of poisonous or decomposed substances to a 
food, with a view to cheating the purchaser, is known as adul- 
teration. Many foods which are artificially manufactured have in 
the past been adulterated to such an extent as to be almost unfit 
to eat, or even harmful. One of the commonest substitutions is 
cheap grape sugar (glucose) for the more expensive cane sugar. 
Glucose, manufactured from corn, is a good food and is not a 
harmful adulterant. It is used largely in candy making. Alum is 



sometimes added to make flour whiter. Probably the food which 
has suffered most from adulteration is milk, as water can be added 
without the average person being the wiser. By means of an inex- 
pensive instrument known as a lactometer, this cheat can easily 
be detected. Before the Pure Food Law was passed in 1906, milk 
was frequently treated with substances like formalin to make it 
keep sweet longer. Such preservatives are harmful, and it is now 
against the law to add anything harmful to any food. 

Coffee, cocoa, and spices have been subject to great adulteration 
because of the ease with which starch, ground-up date or other 
seeds, chicory, and other cheaper substitutes may be added. 
Detection of these adulterations is easily made by means of a com- 
pound microscope. Honey, sirups of various kinds, cider, and 
vinegar have all been found sometimes to be either artificially 
made from cheaper substitutes or to be adulterated with such sub- 
stitutes. The use of butter substitutes is legitimate, when prop- 
erly labeled, but one must remember that pure butter has a 
vitamin content and should be used in every dietary. Lard, 
cottonseed oil, and nut substitutes have a useful place in cooking 
and in salad dressings. 

Stimulants. — We have learned that food is anything that sup- 
plies building material or releases energy in the body ; but some 
materials used by man, presumably as food, do not come under 
this head. Such are tea and coffee. When taken in moderate 
quantities, they produce a temporary increase in the vital activities 
of the person taking them. This stimulation is due to the presence 
of a drug called caffein which acts upon the nervous system as a 
whip acts on a tired horse. In moderation, tea and coffee appear 
to be harmless to most adults. Some people, however, cannot use 
either, even in small quantities, without ill effects. It is the habit 
formed of relying upon the stimulus given by tea or coffee that 
makes them a danger to man. Cocoa and chocolate, although both 
contain a stimulant, are in addition good foods, having from 12 
per cent to 21 per cent of protein, from 29 per cent to 48 per cent 
of fat, and over 80 per cent of carbohydrate in their composition. 

Is Alcohol a Food ? — The question of the use of alcohol is of 
much interest among physiologists and doctors. It is now over 
thirty years since Dr. Atwater of Wesleyan Univ^ersity made his 


experiments by means of the respiration calorimeter, to ascertain 
whether alcohol is of use to the body as food.^ In these experi- 
ments the subjects were given, instead of their daily allotment of 
carbohydrates and fats, enough alcohol to supply the same amount 
of energy that these foods would have given. The amount was 
calculated to be about two and one half ounces per day, about as 
much as would be contained in a bottle of light wine. This alcohol 
was administered in small doses six times during the day. Pro- 
fessor Atwater's results may be summed up briefly as follows : 

1. The alcohol administered was almost all oxidized in the 

2. The potential energy in the alcohol was transformed into heat 
or muscular work. 

3. The body apparently did about as well with the rations in- 
cluding alcohol as it did with other rations. 

This showed that alcohol in small quantities could be used in 
the body as a food. 

On the other hand, we know that although alcohol may techni- 
cally be considered as a food, it has a harmful effect on the body 
tissues which foods do not have. 

Alcohol a Poison. — According to Professor Chittenden, one of 
the great dietary experts of this country, alcohol, although it is 
oxidized in the body, has a harmful effect upon the liver and circu- 
lation, because it reduces the amount of oxidation that takes place 
in the liver and hence throws into the circulation substances like 
uric acid, which are harmful to health. This indicates that alcohol 
is a poison. Furthermore, statistics show conclusively that cer- 
tain diseases, notably cirrhosis of the liver, are greatly increased 
by the excessive use of alcohol. 

A commonly accepted definition of a poison is: any substance 
which, when taken into the body, tends to cause the death of the organ- 
ism or serious detriment to its health. That alcohol may do this is 
well known by scientists. No one who reads of the increase 
in the number of deaths from adulterated or ^' bootleg " liquor 
can draw any other conclusion than that alcohol is a dangerous 

^ Alcohol is made up of carbon, oxygen, and hydrogen. It is very easily oxidized 
but it cannot, as is shown by the chemical formula, be of use to the body in tissue 
building, because of its lack of nitrogen. 


substance, especially in the form in which it is illegally sold by 
" bootleggers." " Home brews " of various kinds often have other 
poisons formed in them, besides alcohol, and thus are doubly dan- 

Dangers from Alcohol. — It is a matter of common knowledge 
that alcohol taken in small quantities does not do any apparent 
harm. But if we examine the vital records of life insurance com- 
panies, we find a large number of deaths directly due to alcohol 
and a still greater number due in part to its use. The poisonous 
effect is not found in a small dose, but repeated small doses ulti- 
mately show their harmful effect. Hardening of the arteries, a 
dangerous disease of middle-age or old age, is often caused by the 
cumulative effect of alcohol. The annual table of deaths from 
alcoholism in large American cities compiled by the Scientific 
Temperance Federation from data furnished by city health officials 
continues to show a smaller number of deaths from this cause than 
in the pre-prohibition period, although there has been an increase 
since the first prohibition years. The following figures represent 
the total deaths from alcoholism in nineteen cities of more than 
300,000 population. These cities included in 1920 about 19,000,- 
000 of the 105,000,000 people in the United States. 

Total Deaths from Alcoholism in Nineteen Large Cities 




....... 321 













The increase in deaths after 1920 is undoubtedly due partly to 
the dangerous quality of bootleg liquor. 

The Effect of Alcohol on the Mortality of Offspring. — Professor 
Laitinen, Dr. Stockard, and other experimenters have worked 
with guinea pigs and white rats to learn if alcohol has any effect 
upon the birth rate and death rate of the offspring. They found 
that the death rate is much higher in the animals born from 
alcoholized parents than in those from non-alcoholized parents. 
The rate of development of the young* is faster in the non-alco- 
holized animals. In other words, the alcoholized animals were not 


Susceptibilty to Disease Increased by Alcohol. — A good many 
experiments have been made which prove that alcohol causes 
increased susceptibility to disease. Recent experiments made by 
Dr. E. G. Stillman at the Rockefeller Institute show that mice 
intoxicated with alcohol have much less resistance to pneumonia 
germs than normal mice. An experiment tried with influenza 
germs showed a similar result. 

Death Rates in Different Occupations. — Recent reports from 
England, where certain occupations give a special temptation to 

drink, show that if 100 be ac- 


m 94 90'/^ WO 90 80'/^ 100 6756 

Effect of tobacco smoking as shown by 
measurements of college students. The 
first, white column represents 100 per 
cent for non-smokers ; the second column, 
the comparison for occasional smokers ; 
and the third, for regular smokers. 

cepted as an average death rate, 
the rate among brewers is 129, 
among hotel keepers 160, and 
among barkeepers 218. On the 
other hand, the death rate 
among clergymen is only 56, for 
agricultural workers 60, and in 
the medical profession 88. 

The Use of Tobacco. — A 
well-known authority defines a 
narcotic as a substance '^ which 
directly induces sleep, blunts the 
senses, and, in large amounts, 
produces complete insensibility J ^ 
Tobacco, opium, chloral, and co- 
caine are examples of narcotics. 
Tobacco owes its narcotic in- 
fluence to a strong poison 

known as nicotine. Its use in killing insect parasites on plants is 
well known. In experiments with jellyfish and other simply organ- 
ized animals, the author has found as little as one part of nicotine 
to one hundred thousand parts of sea water to be sufficient to affect 
profoundly an animal placed within it. Nicotine in a pure form 
is so powerful a poison that two or three drops would be suffi- 
cient to cause the death of a man by its action upon the nervous 
system, especially upon the nerves controlling the beating of the 
heart. This action is well known among boys training for athletic 
contests. The heart is affected and boys become "short-winded'^ 


as a result. It has been demonstrated that tobacco has, too, an 
important effect on muscular development. The stunted appear- 
ance of the young smoker is well known. 

Use and Abuse of Drugs. — A large proportion of the American 
people are addicted to the use of drugs, especially patent medicines. 
A glance at the street-car advertisements shows this. Most of 
the medicines advertised contain alcohol in greater quantity than 










Amounts of alcohol in some liquors and in some patent medicines. 
o, beer, 5%; 6, claret, 8%; c, champagne, 9%; d, whisky, 50%; e, well- 
known sarsaparilla, 18%; /, g, h, much-advertised nerve tonics, 20%, 21%, 
25%; i, another much-advertised sarsaparilla, 27%; j, a well-known tonic, 
28%; fc, I, bitters, 37%, 44% alcohol. 

beer or wine, and many of them have habit-forming drugs in their 

Before the Pure Food and Drug Act went into effect it was 
possible for the makers of patent medicines to sell those con- 
taining alcohol, opium, morphine, and cocaine without the public 
being any the wiser. In consequence, much harm was done by 
the patent medicine industry. Not only were many ''sarsapa- 
rillas" and ''bitters" put on the market, but they were sold to 
persons who were opposed to alcohol. A dose of one of these 
medicines usually contained about as much alcohol as the same 
amount of whisky. Such ''bracers," as the American Medical 
Association have called this type of medicine, were of course habit 


formers. Any one who began to take them soon became depend- 
ent upon them. 

Another more deadly kind of medicine commonly sold is the 
subtle poison acetan'ilid, sl powerful heart depressant contained, 
even at the present time, in a good many of the so-called headache 
powders. Although the Pure Food and Drug Act now requires 
that the label show a statement of the alcohol, acetanilid, cocaine, 
opium, and certain other harmful drugs contained in a "patent 
medicine," many people do not read the label, so the danger con- 
tinues. What is far worse, the use of such drugs often leads to the 
drug habit. There is danger also from prussic acid, arsenic, and 
other deadly drugs not covered by the law. 

Perhaps the worst thing about patent medicines is that they 
rarely cure any one, and they take an immense amount of money 
from people who can ill afford to spend it. Nearly $100,000,000 a 
year is estimated to be spent for patent medicines alone in this 
country. Many ignorant people, incurably ill with tuberculosis 
or cancer, make their condition worse through the purchase of 
cough or cancer cures, which probably contain a habit-forming 
drug or alcohol. Think how much more good the money thus 
spent would have done had it been invested in proper foods and 
good nursing, or in gaining the advice of a physician. 

Every boy and girl should read the booklets of the American 
Medical Association which treat of the various phases of the 
patent medicine evil. Make a collection of the free samples of 
drugs given away and see how many of them are condemned on 
their own labels. Above all, never use drugs except on the advice 
of a reliable physician. 

Summary. — The Pure Food and Drug Act has done some good 
in exposing adulterations and protecting people from the dangers 
of drugs. But education must do more. We must learn, as a 
nation, that drugs should be given only by physicians. The drug 
habit is one of this nation's most serious problems. 

As for the alcohol question, although we have prohibition, we 
know well that alcohol is used to-day by a great many people. 
These people are not only breaking the law but they are also 
taking a foolish risk, because it is certain that a large percentage 
of the liquor illegally sold to-day is impure and far more dangerous 


than in the days before prohibition. Every high school boy and 
girl should fight this disregard of law. 

Problem Questions 

1. What is an adulteration? Give five, different kinds of adulterations. 

2. How does the Pure Food and Drug Act protect you? In what respects 
is it a poor protection ? 

3. Are there any establishments handling foods in your community that 
are not controlled by this act ? 

4. Compare stimulants and narcotics in their effects. 

5. Is alcohol a food ? A poison? Give data. 

6. Classify drug dangers, and show the harm each kind does. 

7. Should patent medicines be used? If so, under what conditions? 

Problem and Project References 

American Medical Association, Nostrums and Quackery. Chicago. 
American Medical Association, The Great American Fraud. Chicago. 
American Medical Association, The Propaganda for Reform in Proprietary 

Medicines. Chicago. 
O'Shea, Tobacco and Mental Efficiency. The Macmillan Company. 


Problems : To learn about digestion by studying — 

(a) The functions of glands. 

(b) The work done in the mouth. 

(c) The work done in the stomach. 

(d) The work done in the small intestine. 

(e) The function of the liver. 

To discover the absorbing apparatus and how it is used. 

Laboratory Suggestions 

Demonstration of the food tube of man (with a manikin) . Comparison with 
the food tube of the frog. Drawing (comparative) of the food tube and diges- 
tive glands of frog and man. 

Demonstration of a simple gland. (Microscopic preparation.) 

Home experiment and laboratory demonstration. The digestion of starch by 
saHva. Conditions favorable and unfavorable. 

Demonstration experiment. The digestion of proteins with artificial gastric 
juice. Conditions favorable and unfavorable. 

Demonstration. An emulsion as seen under the compound microscope. 

Demonstration. Emulsification of fats with artificial pancreatic fluid. 
Digestion of starch and of protein with artificial pancreatic fluid. 

Demonstration. Saponification, or making soaps from fats. 

Demonstration of tripe to show increased surface of the digestive tube. 

Laboratory or home exercise. Make a table showing the changes produced 
upon the nutrients by each digestive fluid, the reaction (acid or alkaline) of 
the fluid, where the fluid acts, and what results from its action. 

Purpose of Digestion. — We have learned that organic food 
substances are found in the leaves of plants. This food must be 
taken to other parts of the plant in order to be used. Before it 
can be transported from one part of the plant to another, it is 
changed by enzymes into a soluble form, so that it can pass from 
cell to cell by the process of diffusion through a membrane. Much 




the same condition exists in animals. In order that food may be 
of use to man, it must be changed into a state that will allow its 
passage in a soluble form through the walls of the alimentary canal, 
or food tube. This is done by the enzymes which cause digestion. 

Alimentary Canal. — In nearly all vertebrate animals, food is 
taken in the mouth and passed through a food tube in which it is 
digested. In vertebrate animals, including man, this tube is com- 
posed of different portions, named, respectively, as we pass from 
the mouth downward, pharynx 
(far'ir)ks), gullet, stomach, small 
intestine, and large intestine. 

Comparison of Food Tubes 
of Frog and Man. — At this 
time it will be wise for each 
member of the class to dissect 
a frog, with a view to compar- 
ing the organs of digestion with 
those in our own bodies. On 
making this comparison, we 
find that part for part they are 
much the same. But we notice 
that the intestines of man, 
both small and large parts, are 
relatively longer than those of 
the frog. We also notice that 
in man the body cavity or space in which the internal organs rest 
is divided into two parts by a wall of muscle, the diaphragm, which 
separates the heart and lungs from the other internal organs. In 
the frog no muscular diaphragm exists. We can also see plainly 
the silvery transparent mes'entery or double fold of the lining of 
the body cavity in which the organs of digestion are suspended. 
Numerous blood vessels can be found especially in the walls of 
the food tube, which carry the digested nutrients to other parts 
of the body. 

Glands and their Work. — In addition to the alimentary canal 
proper, and connected with it, we find a number of digestive glands, 
varying in size and position. In man there are the saFivary glands 
of the mouth, the gastric glands of the stomach, the pancreas 

Digestive tract of a frog and of a man : 
Gul, gullet ; S, stomach ; L, liver ; G, gall 
bladder ; Sp, spleen ; P, pancreas ; SI, 
small intestine ; LI, large intestine ; V, 
vermiform appendix; A, anus. 


Mouth of gland 

Blood vessel 

(par|'kre-as) and the liver, both connected with the small intestine 
by ducts, and the intestinal glands in the walls of the small intes- 
tine. Besides these glands which aid directly in digestion, there 
are several others known as the endocrine (en'd6-ki'in) or ductless 
glands, because they have no ducts or tubes to carry off their 
contents. These glands give theii' secretions, which contain sub- 
stances known as hor'mcrnes, dhectly uito the blood. We shall 
study theii' functions later. 

Structure of Glands. — In its simplest form a gland may be a 
collection of cells which, by means of their own activity, manufac- 
ture and pour out a substance known as a secretion. The nectar 

gland of a flower is such a collection 
of ceUs. In animals, glands are usu- 
ally tubular, such as the gastric gland 
shown on page 153, or like little sacs, 
as illustrated on this page. In aU 
animal glands there is a rich blood 
supply to and from the secreting ceUs 
that line the tubes or sacs, and tiny 
nerves which control the gland ceUs 
and blood supply. 

Enzymes and their Work. — Certain 
gland cells form secretions containing 
the wonderful chemical activators called 
enzymes, which we have ah'eady found 
cause digestion in plants. In animals 
the enzymes secreted by the cells of the 
glands and poured out into the food 
tube act upon insoluble foods so as to change them to a soluble 
form. They are the product of the activity of the ceU, although 
the}^ are not themselves ahve. We do not laiow much about 
enzymes themselves, but we can observe w^hat the}^ do. Some 
enzymes render soluble different foods, others work in the blood, 
still others probably act within the cells of the body as an aid 
to oxidation, when work is done. Enzymes are ver^^ sensitive to 
changes in temperature and to the degree of acidity or alkalinity 
of the material in which they act. We shall find that the enzymes 
from glands in the walls of the mouth will not act long in the 

Diagram of a gland. 



Stomach after the change from an alkaHne surrounding in the 
mouth to an acid surrounding in the stomach. Enzymes seem to 
be able to work indefinitely, provided the surroundings are favora- 
ble. A small amount of digestive enzyme, if it had long enough 
to work, could therefore digest a large amount of food. 

Salivary Glands. — We are all familiar with the substance 
called sali'va which acts as a lubricant in the mouth. Saliva is 
manufactured in the cells of three pairs of glands which empty 
into the mouth, and which are called, according to their position, 
the parot'id (beside the ear), the submaxillary (under the jawbone), 
and the sublin'gual (under the tongue). 

Digestion of Starch. — If we collect some saliva in a test tube, 
add to it a little starch paste, place the tube containing the mixture 


Eusf-achian tube 
■ Esophagus 


Mouth of a frog and mouth of a man. Notice the points of likeness 
and the points of difference. 

for twenty minutes in tepid water, and then test with Fehling's 
solution, we find grape sugar present. Careful tests of the starch 
paste and of the saliva, made separately, show no grape sugar in 

If another test is made for grape sugar, in a test tube containing 
starch paste and saliva as above, and also a few drops of a weak acid, 
it will be found that no starch has been changed to grape sugar. 
You will remember that starch in the growing corn grain was 
changed to grape sugar by an enzyme called diastase. In saliva a 

H. NEW CIV. BIOL. — 11 


similar action is caused by an enzyme called ptyalin (ti'd-lin), or 
salivary am'ylase; but this enzyme acts only in. an alkaline medium 
at about the temperature of the body. 

Mouth Cavity in Man. — In a study of a frog we can find that 
the mouth cavity has six tubes opening from it (figure on page 149) . 
These are (a) the gullet or esoph'agus, (b) the windpipe or trachea 
(tra'ke-d), opening through the glottis, (c) the pair-ed nostril hole^ 
(posterior nares) , (d) the paired Eustachian (u-sta'ki-dn) tubes, lead- 
ing to the ear. All of these 
openings are found also in man. 
In man the mouth cavity 
and the internal surface of 
the food tube are lined with 
mucous membrane. The mucus 
secreted from gland cells in this 
lining makes a slippery surface 
so that the food can slip down 
easily. The roof of the mouth 
is formed by a plate of bone 
called the hard palate, in front, 
and a softer continuation to 
the back, called the soft palate. 
These separate the nose cav- 
ity from that of the mouth. 
The space back of the soft 
palate is called the pharynx, 
or throat cavity. From the 
pharynx lead off the gullet and 
windpipe, the former back of 
the latter. The lower part of 
the mouth cavity is occupied by a muscular tongue. The tongue 
Ls used in moving food about in the mouth, and in starting it on its 
way to the gullet ; it also plays an important part in speaking. 

The Teeth. — In man the teeth, unlike those of the frog, are 
used in the mechanical preparation of the food for digestion. In- 
stead of holding prey, they crush, grind, or tear food so that more of 
its surface may be given for the action of the digestive fluids. The 
first or " milk " teeth of man are only twenty in number, while in 

Mouth cavity of man. e, Eustachian 
tube ; Hp, hard palate ; sp, soft palate ; 
Ut, upper teeth ; Lt, lower teeth ; T, 
tongue ; Ph, pharynx ; Ep, epiglottis ; Lx, 
larynx or voice box ; E, esophagus or 
gullet; Tr, trachea. 



the second or ^' permanent^' set there are thirty-two teeth. These 
teeth are divided, according to their structure, into four groups. 
In the center of each jaw in front are four teeth with chisel-hke 
edges (eight in all) ; these are the inci'sors, or cutting teeth. Next 
to them on each side is a single tooth (four in all) ; these have 
rather sharp points and are called the canines. Then come two 
teeth on each side, eight in all, called premolars. Lastly, at the 
back are the flat-top molars, or grinding teeth, of which there are 
six in each jaw. Food is 
caught between irregular 
projections on the surface 
of the molars and crushed 
to a pulpy mass. 

Each tooth, as the figure 
shows, is composed chiefly 
of hard bone or dentine. 
The crown of the tooth is 
covered with enamel, the 
hardest substance in the 
body. In the interior is 
a pulp cavity, which dur- 
ing the life of the tooth 
contains blood vessels and 
nerves, which give the 
tooth its nourishment. 
The tooth is held in its 
bony socket in the jaw by 

When a tooth dies, bacteria often set up an irritation at its base 
and form a center of focal injection from which a stream of poison 
gets into the blood. As a result of this infection, very serious 
diseases may occur, of which the most common are rheumatism 
of the joints and neuritis or inflammation of the nerves. Infected 
teeth should be extracted, as this removes the cause of the trouble. 

Care of the Teeth. — Too much emphasis cannot be placed on 
the proper care of the teeth, for many ills beside those already 
mentioned may be laid to neglect. The teeth should be care- 
fully brushed each morning and before you go to bed. Use a 

Teeth of the upper jaw, from below. 
1, 2, incisors; 3, canine; 4. 5, premolars; 
6, 7, S, molars. II. longitudinal section of a 


medium stiff brush and work the bristles in a vertical direction 
away from the gum so as to get between the teeth. Dental silk 
should be used after meals. 

It has been recently found that fruit acids are very beneficial to 
the teeth. Vinegar diluted to about half strength with water 
makes an excellent dental wash. If one has an acid mouth, a good 
tooth paste mixed with castile soap may be used. 

The teeth should be cleaned by a reliable dentist at least every 
six months. In this way deposits which cover the teeth may be 
removed and decay prevented. If we allow decay to start, it 
means sooner or later the loss of the tooth. 

Decay usually begins where particles of food lodge. Here 
bacteria feed and pour out substances which act upon the hard 
enamel. Once this is eaten through, decay rapidly advances, and 
before long the ache in the tooth announces that decay is approach- 
ing the pulp cavity. It may then be too late to save the tooth. 
For this reason alone, if for no other, a dentist should frequently 
examine our teeth ; false teeth are a very poor substitute for lost 

Chewing and Swallowing. — Food should simply be chewed and 
relished, with no thought of swallowing. It will be found that if 
you attend only to the agreeable task of extracting the flavors of 
your food, nature will take care of the swallowing, and this will 
become, like breathing, involuntary Thorough mastication takes 
time, therefore one must not feel hurried at meals. 

After food has been chewed and mixed with saliva, it is rolled into 
little balls and pushed by the tongue into such position that the 
muscles of the throat cavity may seize it and force it downward. 
Food, in order to reach the gullet from the mouth cavity, must pass 
over the opening (glottis) into the trachea. When food is in the 
course of being swallowed, the upper part of the gullet forms a 
trapdoor over the opening. When this trapdoor, called the epi- 
glottis, is not closed, and food '' goes down the wrong way," we 
choke, and the food is expelled by coughing. 

The Gullet, or Esophagus. — Like the rest of the food tube, 
the gullet is lined with soft and moist mucous membrane. The 
wall is made up of two sets of muscles, — the inside ones running 
around the tube; the outer layer taking a longitudinal course. 



Opening into 

After food leaves the mouth cavity, it gets beyond our direct con- 
trol, and the muscles of the gullet, stimulated to activity by the 
presence of food in the tube, push the food down by a series of con- 
tractions until it reaches the stomach. These wavelike movements 
(called peristal' tic movements) occur also in other parts of the food 
tube, food being pushed along in the stomach and the small intes- 
tine by a series of these slow-moving muscular waves. Peristaltic 
movement is caused by muscles which are not under voluntary 
nervous control, although anger, fear, or other unpleasant emotions 
have the effect of slowing them or even stopping them entirely. 

Stomach of Man. — The stomach is a pear-shaped organ capable 
of holding about three pints. The end opposite to the gullet, 
which empties into the small intestine, is provided with a ring of 
muscle called the pylo'rus. When this muscle relaxes, it permits 
the passage of food from the stomach. 
There is also another ring of muscle 
guarding the entrance to the stomach. 

Gastric Glands. — If we open the 
stomach of a frog and remove its contents 
by careful washing, its wall is seen to be 
thrown into folds internally. Between 
the folds in the stomach of man, as well 
as in the frog, are 1 ocated a great number 
of tiny pits. These form the mouths of 
the gastric glands, which pour into the 
stomach a secretion known as the gastric 
juice. The gastric glands are little tubes, 
the lining of which secretes the fluid. 
When we think of or see appetizing food, 
this secretion is given out in considerable quantity. The stomach, 
like the mouth, " waters " at the sight of food, as the glands are 
controlled by nerves. Gastric juice is slightly acid in its chemical 
reaction, containing about 0.2 per cent free hydrochloric acid. It 
also contains two enzymes : one very important, called pepsin^ and 
the other, less important, called rennin. Rennin curdles or coagu- 
lates a protein found in milk ; after the milk is curdled, the pepsin 
is able to act upon it. " Junket " tablets, which contain rennin, 
are used sometimes in the preparation of a dessert from milk. 

Neck of 

H CI secreting eel/ 
on inner margin 
of gland 

Cells secreting 
fluid containing 

Body of gland 
where most of 
secreting is 

A gastric gland. 


Action of Gastric Juice. — If proteins are treated with artificial 
gastric juice at the temperature of the body, they will become swol- 
len and then gradually change to substances (peptones) which are 
soluble in water. This is due to the action of the enzyme pepsin. 

The hydrochloric acid found in the gastric juice acts upon lime 
and some other salts taken into the stomach with food, changing 
them so that they may pass into the blood and eventually form 
the mineral part of bone or other tissue. This acid also has a 
decided antiseptic influence in preventing growth of bacteria, some 
of which cause decay, while others cause disease. 

Experiments on Digestion in the Stomach. — Some very interest- 
ing experiments have been made by Professor Cannon of Harvard 
with reference to the movements of the stomach contents. Cats 
were fed with a material having in it subnitrate of bismuth, a 
harmless chemical that is visible under the fluoroscope. It was 
found that shortly after food reached the stomach, a series of 
waves began which sent the food toward the pyloric end of the 
stomach. If the cat was feeling happy and well, these contrac- 
tions continued regularly, but if the cat was cross or bad tempered, 
the movements would stop. These experiments were repeated on 
men, with like results, and show the importance of cheerfulness 
at meals. Other experiments showed that food which was churned 
into a soft mass was permitted to leave the stomach only when 
it became thoroughly permeated by the gastric juice. It is the 
acid in the partly digested food that causes the pyloric ring of 
muscle to open and allow the food to escape little by little into the 
small intestine. 

Position and Structure of the Pancreas. — The partly digested 
food in the small intestine almost immediately comes in contact 
with secretions from the liver, the pancreas, and the intestinal 
glands. We shall first consider the function of the pancreas. The 
pancreas is one of the most important digestive glands in the 
human body. It is a rather diffuse structure, resembling the 
salivary glands. Its duct (joined with the bile duct from the 
liver) empties into the small intestine a short distance below 
the pylorus. 

Work done by the Pancreas. — Starch paste added to artificial 
pancreatic fluid and kept at blood heat is soon changed to sugar. 



Proteins, under the same conditions, are broken down into amino- 
acids. Fats, which so far have been unchanged except to be 
melted by the heat of the body, are changed by the action of 
the pancreatic fluid and the bile into substances which can pass 
through the walls of the food tube. If we test pancreatic fluid, 
we find it strongly alkaline in its reaction. If two test tubes, one 
containing olive oil and water, the other olive oil and a weak 
solution of caustic soda (which has an alkaline reaction) arc 
shaken violently and then 
allowed to stand, the oil and 
water will quickly separate, 
while the oil and solution of 
caustic soda will remain for 
some time in a milky emul- 
sion. If this emulsion is ex- 
amined under the microscope, 
it will be found to be made of 
millions of little droplets of 
fat, floating in the liquid. 
The presence of the caustic 
soda helped the forming of the 
emulsion. Pancreatic fluid 
emulsifies fats and changes 
them into fatty acids and 
soft soaps. Fat in these forms 
can be absorbed. The above 
changes are brought about by 
three enzymes, amylase, which 

breaks down starches to simpler sugars ; try p^ sin, which, working 
with other enzymes of the small intestine, breaks protein into 
amino-acids ; and lip'ase, which breaks the fats into fatty acids 
and glycerin. These fatty acids become soap when mixed with the 
alkaline material in the intestinal juice. 

Conditions in which the Pancreas does its Work. — The secre- 
tion of the pancreatic juice is brought about by the action of a 
hormone called secre'tin} This substance, which is formed in some 
of the cells lining the small intestine just below the pylorus, is 

1 See page 148- 

Appearance of milk under the micro- 
scope, showing the natural grouping of the 
fat globules. In the circle a single group 
is highly magnified. Milk is one form of 
an emulsion. (S. M. Babcock, Wis. Bui. 
No. 61.) 


released into the blood at the time food passes from the stomach 
through the pylorus. This food is acid, and the acid, on striking 
the lining of the small intestine, causes the formation of secretin 
in its walls. This secretin passes into the blood and stimulates the 
pancreas and liver to release their fluids. 

Liver. — The liver is the largest gland in the body. In man, it 
hangs just below the diaphragm, a little to the right side of the 
body. During life, its color is deep red. It is divided into three 
lobes, between two of which is the gall bladder, sl thin-walled sac 
which holds the hile, a secretion of the liver. Bile is a strongly alka- 
line fluid of golden brown color. It reaches the intestine through 
the same opening as the pancreatic fluid. Almost one quart of 
bile and about a pint of pancreatic fluid are passed daily into the 
digestive canal. The color of bile is due to certain waste sub- 
stances which come from the destruction of worn-out red cor- 
puscles of the blood. This destruction takes place in the liver 
(and also in the spleen, a large ductless glandlike organ near the 

Functions of Bile. — The liver is not primarily a digestive gland. 
Bile contains no, although it may have the power of ren- 
dering more active the enzyme in the pancreatic fluid that acts 
upon fats. Certain substances in the bile aid especially in the 
absorption of fats Bile seems to be mostly a waste product from 
the blood. It stimulates the peristaltic movements of the intes- 
tine, thus preventing extreme constipation. It also has a slight 
antiseptic effect in the intestine. 

The Liver a Storehouse. — Perhaps the most important func- 
tion of the liver is the formation and storing of a material called 
gly'cogen, or animal starch. The liver is supplied with blood from 
two sources. Some comes from the heart, but a greater amount 
comes directly from the walls of the stomach and intestine. The 
liver normally contains about one fifth of all the blood in the 
body. This blood is very rich in food materials, and from it the 
cells of the liver take out sugars to form glycogen.^ Glycogen is 
stored in the liver until such a time as a food is needed that can be 
quickly oxidized; then it is changed to sugar and carried off by 

1 It is known that glycogen may be formed in the body from protein, and possibly 
from fatty foods. 



the blood to the tissue which requires it, and there used for this 
purpose. Glycogen is also stored in the muscles, where it is oxi- 
dized to release energy when the muscles are exercised. 

The Intestinal Fluid. — Within the waU of the small intestine 
are numerous glands which pour out a fluid known as the succus 
enter'icus. Its functions are not well known, but it contains at 
least one hormone and several enzymes with which it assists the 
pancreatic fluid to do its work. The remaining peptones are broken 
up into amino-acids by the enzyme erep'- 
sin, while maVtase, su'crase, and lac'tase 
change malt sugar, cane sugar, and milk 
sugar to the simplest or single sugars (so 
called because of the molecule C6H12O6). 

Structure of the Small Intestine. — 
The small intestine in man is a slender 
tube nearly twenty feet in length and 
about one inch in diameter. As one of 
the chief functions of the small intestine 
is that of absorption, we must look for 
adaptations which increase the absorbing 
surface of the tube. This end is gained 
in part by the inner surface of the tube 
being thrown into transverse folds which 
not only retard the rapidity with which 
food passes down the intestine, but also 
give more absorbing surface. But far 
more important for absorption are mil- 
lions of little projections which cover the 
inner surface of the small intestine. 

The Villi. — So numerous are these projections that the whole 
surface presents a velvety appearance. Collectively, these struc- 
tures are called the villi (sing, villus) . They form the chief organs 
of absorption in the intestine, several thousand being distributed 
over every square inch of surface. By means of the folds and 
the villi the small intestine is estimated to have an absorbing sur- 
face equal to twice that of the surface of the body. Between the 
villi are found the openings of the intestinal glands which secrete 
the succus entericus. 

Diagram of wall of small 
intestine, greatly magnified. 

a, mouths of intestinal glands ; 

b, villus cut lengthwise to 
show blood vessels and lacteal 
(in center) ; e, lacteal sending 
branches to other villi ; i, in- 
testinal glands ; m, artery ; 
V, vein ; I, t, muscular coats 
of intestine wall. 


lor vena 

Internal Structure of a Villus. — The internal structure of a 
villus is best seen in a longitudinal section. We find the outer wall 
made up of a thin layer of cells, the epithe'lial layer. It is the duty 
of these cells to absorb the fluid food from within the intestine. 
Underneath these cells lies a network of very tiny blood vessels 
and in the core of the villi are spaces which, because of their white 
appearance after the absorption of fats, have been called lac'teals. 
Absorption of Foods. — While diffusion and osmosis are important 
factors in the passage of food and water through the walls of the 

intestine, most physiologists 
agree that the living matter 
in the cells lining the villi 
exerts a selective action on 
the substances that pass into 
the blood and lacteals. The 
cells act as tiny chemical 
laboratories, actually allow- 
ing some food substances to 
pass through them and with- 
holding the passage of others. 
Fats, for example, are built 
up again in these cells from 
fatty acids and glycerin, and 
in the form of fats are passed 
into the central part of the 
villus, eventually reaching 
the blood by v/ay of the 
lacteals and the thoracic duct 
without passing through the 
liver. (See diagram.) On 
the other hand, simple sugars 
and amino-acids pass directly into the blood and reach the portal 
circulation. These pass through the liver, where, as we have seen, 
sugar is taken from the blood and stored as glycogen. From the 
liver, the food within the blood is carried to the heart, pumped to 
the lungs, returned to the heart, and is pumped to the tissues of the 
body. A large amount of water and some salts are also absorbed 
through the walls of the stomach and intestine. 

Mesenhric y€[i 


Diagram showing how nutrients reach the 


Large Intestine. — The large intestine has somewhat the same 
structure as the small intestine, except that it lacks the vilU and 
has a greater diameter. Considerable absorption, however, takes 
place through its walls as the mass of food and refuse material is 
slowly pushed along by the peristaltic movements of the muscles 
within its walls. 

Vermiform Appendix. — At the point where the smaU intestine 
widens to form the large intestine, a baglike pouch is formed. 
From one side of this pouch is given off a small tube, usually about 
four inches long, closed at the lower end. This tube, the rudiment 
of what is an important part of the food tube in the lower verte- 
brates, is called the vermiform appendix. It has come to have un- 
pleasant notoriety, as the site of many cases of serious inflammation. 

Constipation. — In the large intestine live billions of bacteria, 
some of which make and give off poisonous substances known as 
toxins. These substances are easily absorbed through the walls 
of the large intestine, and, when they pass into the blood, cause 
headaches and sometimes serious trouble. Hence it follows that 
the lower bowel should be emptied of this matter as frequently as 
possible, at least once a day. Constipation is one of the most 
serious evils the American people have to deal with, and it is 
largely brought about by the artificial life we lead, with its wrong 
kinds of food and its lack of exercise, fresh air, and sleep. Fruit 
with meals, especially at breakfast, plenty of water between meals 
and before breakfast, and plenty of fresh vegetables and cereals 
to supply the roughage or waste material sufficient to stimulate 
the muscles of the lower bowel, all will aid in preventing consti- 
pation. Exercise, particularly of the abdominal muscles, and 
regular toilet habits will also help to correct this evil. 

Hygienic Habits of Eating ; the Causes and Prevention of Dys- 
pepsia. — From the contents of this chapter it is evident that 
the object of the process of digestion is to break up solid food 
so that it may be absorbed to form part of the blood. Any habits 
we may form of thoroughly chewing our food will evidently 
aid digestion. The smaller the pieces of food the more surface 
will be presented to the digestive fluids containing the enzymes 
and the more complete will be the digestion. Undoubtedly much 
of the distress known as dyspepsia is due to hasty meals with 


consequent lack of proper chewing of food. The message of Mr. 
Horace Fletcher in bringing before us the need of proper mastica- 
tion of food and the attendant evils of overeating is one which we 
cannot afford to ignore. It is a good rule to go away from the table 
feeling a little hungry. Eating too much overtaxes the digestive 
organs and prevents their working to the best advantage. Still 
another cause of dyspepsia is eating when in a fatigued condition. 
It is always a good plan to rest a short time before eating, especially 
after any hard manual work. We have seen how great a part 
unpleasant emotions play in preventing peristaltic movements of 
the food tube. Conversely, pleasant conversation, laughter, and 
fun will help you to digest your meal. Eating between meals is 
condemned by physicians because it calls the blood to the digestive 
organs at a time when it should be more active in other parts of 
the body. The excessive use of ice cream sodas and other drinks 
is bad for this reason and because it dulls appetite for regular 
meals. Good habits of eating will go far in keeping one healthy. 

Place wheee 

Digestion is 





End Product 




















Ren n in 


Casein of 

























Fatty acid 












and pro- 















Cane sugar 









Milk sugar 






Summary. — Digestion is the process by means of which foods 
are prepared to become part of the blood. This is brought 
about by enzymes, agents which cause complex foods to break down 
into simple forms which are capable of absorption through the 
cells lining the food tube. 

The table on page 160 sums up the process of digestion in the 
human body. 

Absorption takes place mostly in the small intestine by means 
of very numerous absorbing organs called villi. Absorption is 
more than diffusion or osmosis, as the cells of the villus appear to 
have a selective action on the solutes absorbed. 

Problem Questions 

1. How is digestion brought about? 

2. What is an enzyme? How is it made? How does it work? Name 
some enzymes and give their functions. 

3. Compare the mouth of the frog and of man in all respects. 

4. Discuss the teeth as to function, structure, and care. 

5. What is the function of the tongue in digestion ? Of the saUvary glands ? 

6. What are the functions of the stomach ? How are they accomphshed ? 

7. What are hormones and what do they do? 

8. What is secretin and how does it function? 

9. Why is the pancreas considered the most important digestive gland? 

10. What are the fimctions of the liver? 

11. What is glycogen and where is it made? 

12. What is the result of final digestion on foods? 

13. How and where is food absorbed ? 

Peoblem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Burton-Opitz, Physiology. W. B. Saunders Company. 

Cohnheim, Enzymes. John Wiley and Sons. 

Harrow, Glands in Health and Disease. E. P. Du^ton and Company. 

Martin, The Human Body, Advanced Course. Henry Holt and Company. 

Schafer, The Endocrine Organs. Longmans, Green and Company. 

Starling, Principles of Human Physiology. Lea and Febiger. 

Stiles, Nutritional Physiology. W. B. Saunders Compan3^ 

XJnderhill, The Physiology of the Amino-acids. Yale University Press. 

Williams, Anatomy and Physiology. W. B. Saunders Company. 


Problems : To discover the composition and uses of the different 
parts of the blood. 

To find out the means by which the blood is circulated through the 

To study the ductless glands and their secretions. 

Laboratory Suggestions 

Laboratory demonstration. Structure of blood, fresh frog's blood and human 
blood. Drawings. 

Laboratory demonstration. Clotting of blood. 

Laboratory demonstration. Use of models to demonstrate that the heart 
is a force pump. 

Laboratory demonstration. Capillary circulation in the web of a frog's foot 
or a tadpole's tail. Drawing. 

Home or laboratory exercise. The relation of exercise to the rate of heart beat. 

Composition of the Blood. — We learned in the last chapter that 
the chief function of the digestive organs is to change foods so 
that they can pass into the blood. The chemical composition 
of the blood is very complex and varies in different parts of the 
body. The fluid part is the plasma, which consists of water 
(about 90 per cent) and the various organic food substances (about 
10 per cent) digested sugars, fats, and amino-acids, mineral salts, 
and numerous other substances, among which are enzymes and 
hormones. The blood also holds three kinds of bodies, the red 
corpuscles, the colorless corpuscles, and the blood plates. 

The blood is the great go-between connecting the outside world 
and the body cells. It carries gases to and from the cells; it 
carries the chemical messengers, the mysterious hormones, which 
play so important a part in our bodily activity ; it carries the 
an'tibodies of various kinds which fight diseases ; it carries the 
red and the colorless corpuscles, which are so necessary to our very 






Red corpuscle of a man compared with that of 
a frog. 

lives ; and it carries food to the body cells. In the cells work is 
performed, oxidation takes place, and heat is released as energy. 
The almost constant temperature of the body is also due to the 
blood, which brings to the surface of the body the excess heat 
given off by the oxidation of food in the muscles and other tissues. 
The Red Blood Corpuscle, its Structure and Functions. — The 
red corpuscle in the blood of the frog is a true cell of disk-hke form, 
containing a nucleus ; while 
that of man is in the form 
of a biconcave disk, without 
a nucleus. So small and so 
numerous are these corpus- 
cles that about five million 
of them are found in a 
cubic millimeter of nor- 
mal blood. Their color, a 
dirty yellow when separate 

corpuscles are viewed under the microscope, is due to an iron- 
protein combination called hcemoglo'hin. Haemoglobin will combine 
chemically with oxygen, forming a bright red compound called 
oxyhcemoglohin. In the parts of the body where oxidation is 
going on, the red corpuscle releases its load of oxygen and takes 
ap in exchange carbon dioxide. This results in a change of color 
to dull red. Thus the red corpuscles are gas carriers. 

The Colorless Corpuscle, Structure and Functions. — The color- 
less corpuscles, of which several kinds are found in the blood, are 

irregular in outline, as 
they constantly change 

^ , ^^ , I — . their form. The color- 

Lymphocyte Polynudedr /eucocyrej , , , 

'^ 1^ ^ ^ less corpuscles are less 

Two kinds of colorless corpuscles. numerous than the red, 

the ratio being about 1 to 700 in a normal person. They greatly 
increase in number in certain diseases. They have the power of 
movement, for they are found not only inside but also outside the 
blood vessels, showing that they have worked their way between 
the cells that form the walls of the blood tubes. 

A Russian zoologist, Metch'nikoff, after studying a number of 
simple animals, such as medusae and sponges, found that in such 


animals some of the ceUs lining the inside of the food cavity take 
up or engulf minute bits of food. Later, this food is changed into 
the protoplasm of the cell. Metchnikoff beUeved that the colorless 
corpuscles of the blood have somewhat the same function. This 
has been found to be true, for, hke the amoeba, they feed by en- 
gulfing their prey. This fact has a very important bearing on the 
relation of colorless corpuscles to certain diseases caused by bacteria 
within the body. If, for example, bacteria get into a wound, 
inflammation may set in. Colorless corpuscles called phag'ocytes 

at once surround the spot and 
attack the bacteria which cause 
the inflammation. The blood 
contains certain anti-bodies 
called op^sonins which, when 
^~ , ^ 1 ^. 1 • present, enable the corpuscles 

Colorless corpuscle attacking germs. ^ ' ^ 

to enguK and digest the bac- 
teria. If the bacteria are few in number, they are quickly 
destroyed. If bacteria are present in great quantities, they may 
prevail and kill the phagocytes. The dead bodies of the pha- 
goc>i;es thus killed are found in the pus, or matter, which ac- 
cumulates in infected wounds. In such an event, we must come 
to the aid of the colorless corpuscles by washing the wound with 
some antiseptic, as weak carbohc acid, lysol, hydrogen peroxide, 
or zonite. 

Plasma and the Clotting of Blood. — If fresh beef blood is 
allowed to stand over night, it wiH be found to have separated into 
two parts, a dark red, almost sohd clot, and a thin, straw-colored 
Hquid called se'rum. 

If fresh beef blood is poured into a pan and briskly whipped with 
a bundle of httle rods (or mth an egg beater) , a stringy substance 
will stick to the rods. This, if washed carefully, is seen to be 
almost colorless. Tested with nitric acid and ammonia, it is found 
to contain a protein substance. This is called fi'hrin. 

In blood within the circulatory system of the body, the fibrin 
is held in a fluid state called fibrin'ogen. Blood plasma, then, is 
made up of serum and of fibrinogen, which coagulates when blood 
is removed from the blood vessels, entangles blood corpuscles, and 
thus forms a blood dot. The clotting of blood is of great physio- 



logical importance, for otherwise we might bleed to death even from 
a small wound. 

Blood Plates. — A substance called throm'hin is the active agent 
in changing fibrinogen to the insoluble fibrin of a clot. This 
change seems to be due to the action of minute bodies in the blood 
known as hlood plates. Under abnormal conditions these blood 
plates break down, releasing some substances which eventually (if 
the blood has the necessary content of calcium) cause the thrombin 
to do its work. 

Disease-resisting Functions of the Plasma. — It is common 
knowledge that some of us '* take " catching or communicable dis- 
eases more easily than others. Some 
fortunate persons are immune to certain 
diseases, that is, they do not take them, 
because certain antibodies are present in 
their blood. These antibodies act in dif- 
ferent ways, but their work is directed 
against bacteria which get into the body 
and cause disease. Some antibodies, 
called ly'sins, have the power to dissolve 
cells. Others, called aggWtinins, cause 
the bacteria in the blood to become stuck typhoTd germs dump together 

together in little inactive masses, so that when added to the serum of a 
.^ r J.1 1 X person who has typhoid. 

they are an easy prey tor the phagocytes. 

We have aheady heard of the work of the opsonins, another 
kind of antibody. Agglutinins and other kinds of antibodies 
called precip^itins have become a great help to physicians in de- 
termining whether a person has a given disease. For example, 
a test known as the Widal (ve-daF) test is now used in all hos- 
pitals to determine if a person has typhoid fever. A few drops 
of blood from the patient is allowed to stand until the serum 
has separated, this is then diluted with a weak salt solution and 
to this are added some living typhoid bacteria. If the person 
has typhoid, the bacteria added to his serum will immediately 
become agglutinated, thus showing that his antibodies are already 
formed and at work. This is only one of a number of tests that 
have been developed in recent years. Just as each disease is 
caused by a specific kind of organism, producing a specific kind 

H. NEW CIV. BIOL. — 12 

In the Widal test, free 
swimming, widely separated 


of toxin or poison, so the blood forms specific antibodies to fight 
each kind of organism or its toxins. 

Blood Transfusion. — It has been found that there are four types 
of human blood. One type includes about 50 per cent of all 
people. After heavy losses of blood as in an accident or in an 
operation, and in some illnesses, blood is injected into a vein of 
the patient by transfusion from an artery of a volunteer. Before 
this operation is performed, it is necessary to make a test to see if 
the two persons have blood of the same type. This is done by 
means of the agglutinin test : Red corpuscles of the person who is 
to give the blood are added to the blood of the patient. If the red 
corpuscles are agglutinated, then the bloods are of two different 
types and transfusion cannot be made. Lysins may also be present 
that dissolve foreign red corpuscles; hence they are called 
hcBmoly' sins. Tests maj^ be made for these hsemolysins by adding 
washed red corpuscles of the volunteer's blood to the serum of the 
patient's blood. If the corpuscles are dissolved, this blood cannot 
be used for transfusion. 

The Ductless or Endocrine Glands and their Secretions. - - In 
addition to all the functions already mentioned, the blood has 
another very wonderful work. We have already read about the 
hormones (Gr. hormon, exciting), the chemical messengers or regu- 
lators produced by the ductless or endocrine glands in various parts 
of the body. The blood is the only means of communication be- 
tween these glands and the tissues on which their hormones act. 
Scientists are just beginning to understand the tremendous influ- 
ence on life of some of these glands, among which are the thy'roid, 
parathyroid, and thy'mus, small glands located in the neck; the 
adre'nal and suprare'nal bodies, little glands, closely attached 
to the kidneys ; the "pitu'itary body, at the base of the brain ; parts 
of the pancreas; and parts of the egg-producing and sperm-produc- 
ing organs, the o' varies and testes (tes'tez). 

The Thyroid. — It has been found, for example, that under- 
secretion of the thyroid gland is responsible for the condition known 
as cre'tinism, and that this condition can be cured by supplying 
the patient mth th3T:"oid secretion, either by grafting a new thyroid 
of another animal or by injecting or feeding with thyroid extract. 
Overactivity of this gland produces exophthaVmic goiter, a condition 


of extrsme nervousness, with loss of weight and other symptoms, 
such as protruding eyeballs and irregular heart action. The 
thyroid evidently has much to do in regulating the metabolic 
processes within the cells of the body. 

The Adrenals (Suprarenals). — The adrenals, or suprarenals, 
form substances which act upon the muscles and the nervous sys- 
tem. The hormone known as adre'nine causes a faster beating of 
the heart, a heightened blood pressure, and other indications of 
increased muscular activity. It is indeed the emergency hormone 
of the body. It is this hormone that enables the sprinter to make 
his final burst of speed at the tape, or the football player to make a 
desperate stand when almost exhausted. It explains the '^ strength 
of desperation." Adre'naline, an artificial adrenine made by 
chemists, is used in medicine to contract the blood vessels and 
hasten the clotting of blood, and in other ways. 

The Thymus and Pituitary. — The thymus gland, which grows 
smaller or disappears in adult life, seems in some way to regulate 
body growth and metabolism. The pituitary gland also has much 
to do with body size, as dwarfs appear to lack this gland, while in 
giants it seems always abnormally large. Dr. Harvey Gushing of 
the Harvard Medical School, who is an authority on the work of 
the pituitary body, says : '' The Lewis Garroll of to-day would 
have Alice nibble from a pituitary mushroom in her left hand and 
a lutein [a pigment obtained from a portion of the ovary] in her 
right hand and presto ! she is any height desired." 

The Reproductive Glands. — Some part of the ovaries and testes 
have long been known to control the so-called secondary sex charac- 
teristics which give us the outward appearance of females or males. 
It is not too much to say that hormones are responsible for many 
sex characteristics, as experiments with fowls and other animals 
have proved. But popular statements on the effect of grafting 
glands from other animals in human beings are greatly exaggerated 
and can be for the most part disbelieved. 

The Pancreas and Liver. — It has been known for many years that 
the pancreas produces another secretion besides that which passes 
into the digestive tract. But only recently has it been discovered 
that this internal secretion, with its hormone, is produced in 
groups of cells known as the Islands of Langerhans (lang'er-hans) 








Course of lymph 




in the pancreas. If this hormone is not present, then sugar, which 
normally is stored in the liver as glycogen, is allowed to go directly 
into the blood, where it soon appears in excessive quantities, 
causing a disease called diabetes (di-d-be'tez) . Recent work by 
Dr. Banting and his co-workers of Toronto University has resulted 
in the production of the substance in'sulin, which contains the 
hormone. Now a person whose pancreas has lost the power to 
regulate the storage of glycogen in the liver may find relief through 

a proper diet of carbohydrates and 
insulin in prescribed doses. 

Function of Lymph. — The tis- 
sues and organs of the body are 
traversed by a network of tubes 
which carry the blood. Outside 
the blood tubes, in spaces between 
the tissue cells, is another fluid, 
which in chemical composition is 
very much like plasma of the blood. 
This is the lymph. It is, in fact, 
fluid food in which some colorless 
corpuscles, or leucocytes, are found. 
Blood gives up its food material to 
the lymph. This it does by passing 
food through the walls of the capil- 
laries. The food is then given up 
to the tissue cells, which are bathed 
by the lymph. 

Lymph, then, consists of blood 
plasma plus some colorless corpuscles 
which have made their way out between the cells forming the walls 
of the capillaries. It acts as the medium of exchange between the 
blood proper and the cells in the tissues of the body. By means of 
the food supply thus brought, the cefls of the body are able to 
grow, the fluid food being changed to the protoplasm of the cells. 
By means of the oxygen brought by the red blood corpuscles and 
passed over through the lymph, oxidation may take place within 
the cells. Lymph not only gives food to the cells of the body, 
but also takes away carbon dioxide and other waste materials, 

%\Of/)enY dsfe- 


Lj-mph acts as the medium of ex- 
change between the blood and the 
cells of the body. 






A vein 


An artery 

A capillary 

which are ultimately passed out of 

the body by means of the lungs, 

skin, and kidneys. 

Circulation of the Blood in Man. 

— The blood is the carrying agent 

of the body. Like a railroad sys- 
tem, it takes materials from one 

part of the human organism to an- 
other. This it does by means of 

the organs of circulation, — the 

heart and blood vessels. These 

blood vessels are of three kinds : 

the arteries which carry blood away 

from the heart, the veins which 

bring blood back to the heart, and 

the capillaries which connect the 

smallest arteries with the veins. 

The organs of circulation thus 

form a system of connected tubes 

through which the blood flows. 

The Structure of the Heart. — The heart is a cone-shaped mus- 
cular organ about the size of the fist. It is surrounded by a loose 

membranous bag called the pericar'dium, 
the inner lining of which secretes a fluid 
in which the heart lies. 

If we should cut open the heart of a 
mammal down the midline, we could 
divide it into a right and a left side, each 
of which has no internal connection with 
the other. Each side has an upper thin- 
walled portion with a rather large in- 
ternal cavity, the auWicle, which opens 
into a lower portion with heavy muscu- 
lar walls, the ven'tricle. Communication 
between auricles and ventricles is regu- 
lated by little flaps or valves. The 

auricles receive blood from the veins and pass it into the ventricles, 

which pump the blood into the arteries. 

Structure of artery, vein, and 

Diagram of the heart, showing 
the front half cut away. 



The Heart in Action. — The heart is constructed on the same 
plan as a force pump, the valves preventing the reflux of blood 
into the auricles when it is forced out of the ventricles. Blood 
enters the auricles from the veins because the muscles of that part 
of the heart relax; this allows the space within the auricles to 
fill. Almost immediately the muscles of the ventricles relax, thus 

allowing blood to pass into 
the chambers within the 
ventricles. Then, after a 
short pause, during which 
time the muscles of the 
heart are resting, a wave 
of muscular contraction 
begins in the auricles and 
ends in the ventricles, with 
a sudden strong contrac- 
tion which forces the blood 
out into the arteries. 
Blood is kept from flowing 
backward by the valves, 
which act in the same 
manner as do the valves 
in a pump. The blood is 
thus made to pass into 
the arteries upon the con- 
traction of the ventricle 
The Course of the Blood in the Body. — Although the two sides 
of the heart are separate and distinct from each other, yet every 
drop of blood that passes through the right heart also passes 
later through the left heart. There are two distinct systems of 
circulation in the body. The puVmonary circulation takes the 
blood through the right auricle and ventricle, to the lungs, and 
passes it back to the left auricle. This is a relatively short cir- 
culation, in which the blood receives oxygen in the lungs and gives 
up carbon dioxide. The greater circulation is known as the sys- 
temic circulation; in this system, the blood leaves the left ven- 
tricle through the great dorsal artery called the aor'ta. Through 

The heart compared with a force pump. 


I, diagram of side view of the main vessels of the circulatory system of a fish ; 11^ 
similar diagram of a frog ; III, front view of the human circulatory system, with the 

L, Hver ; G, gills ; Lu, lungs ; D, part of the digestive tract ; K, kidney ; A, auricle ; 
V, ventricle ; C, typical group of capillaries in the body tissues. 

In the color scheme red represents aerated blood, as seen in the arteries of the 
body ; blue, the blood carried in the veins of the body. The structures colored dark 
yellow are the lymph vessels. 




smaller and smaller, ever-branching arteries, a large part of the 
blood passes directly to the muscles ; some of it goes to the nerv- 
ous system, kidneys, skin, and other organs of the body. It gives 
up food and oxygen in these tissues, receives the waste products 
of oxidation while passing through the capillaries, and returns to 
the right auricle through two large vessels known as the vence cavce. 
It requires only from twenty to thirty seconds for the blood to 
make the complete circulation from the ventricle back again to 
the starting point. This means that the entire volume of blood 
in the human body passes through the various organs of the body 
three or four thousand times a day.^ 

Portal Circulation. — Some of the blood, on its way back to the heart, 
passes to the walls of the food tube and to its glands. From there it is sent 
with its load of absorbed food to the liver. Here the vein which carries the 
blood (called the portal vein) breaks up into capillaries around the cells of the 
liver, where it gives up sugar to be stored as glycogen. From the liver, blood 
passes directly to the right auricle. The portal circulation connects the stomach 

and the small intestine with the liver. 
It is the only part of the circulation 
where the blood passes through two sets 
of capillaries on its way from auricle to 

Circulation in the Web of a Frog's 
Foot. — If the web of the foot of a live 
frog or the tail of a tadpole is examined 
under the compound microscope, a net- 
work of blood vessels will be seen. In 
some of the larger vessels the corpuscles 
are moving rapidly and in spurts ; these 
are arteries. The arteries lead into 
smaller vessels hardly greater in diameter 
than the width of a single corpuscle. 
These are capillaries, which may be fol- 
lowed into larger veins, in which the blood moves regularly. This illustrates 
the condition in any tissue of man where the arteries break up into capillaries, 
which unite to form veins. 

Structure of the Arteries, Veins, and Capillaries. — A distinct difference in 
structure exists between the arteries and the veins in the human body. The 
arteries, because of the greater strain received from the blood which is pumped 
from the heart, have thicker muscular walls, and in addition are very elastic. 
(See figure on page 169.) Veins are much thinner-walled than arteries and 

1 See Hough and Sedgwick, The Human Mechanism, page 136. 

Capillary circulation in the web of 
a frog's foot, as seen under the com- 
pound microscope. 




Valves in a 
vein. (Explain 
from the text.) 

have small valves which open in the direction of the blood flow. In the figure 
1 is a diagram of a section of a vein when the blood flows properly ; 2, when 
the blood is checked (valve closed) ; 3, valves as they appear in 
a vein cut open. Capillaries are a network of very thin-walled 
vessels through which food, oxygen, and colorless corpuscles 
pass out to the tissues. 

Cause of the Pulse. — The pulse, which can easily be de- 
tected by pressing the large artery in the wrist or the small 
one in front of and above the external ear, is caused by the 
gushing of blood through the arteries after each pulsation of 
the heart. As the large arteries pass away from the heart 
and divide, the diameter of each individual artery becomes 
smaller. At the very end of their course, these arteries are so 
small as to be almost microscopic in size and are very nu- 
merous. There are so many that if they were placed together, 
side by side, their united diameter would be much greater 
than the diameter of the large artery {aorta) which passes 
blood from the left side of the heart. This fact is of very great importance, 
for the force of the blood as it gushes through the arteries becomes very much 

less when it reaches the smaller ves^ 
sels. This gushing movement is 
quite lost when the capillaries are 
reached, first, because there is so 
much more space for the blood to 
fill, and second, because there is con- 
siderable friction caused by the very 
tiny diameter of the capillaries. In 
the veins the blood pressure is more 
uniform and the movement of the 
blood slower than in the arteries. 
It is estimated that blood in the 
large arteries travels about 16 inches 
a second, in the capillaries from ^ 
to ^ of an inch a second, and in the 
large veins about 4 inches a second. 
This shows us that there is a very 
ninV ^^^B ^^ considerable pressure exerted by the 
Inlv ^9^^ blood on the arterial walls at each 

^mPW ^ stroke of the heart. 

Lymph Vessels. — The lymph is 
collected from the various tissues of 
the body by means of a number of 
very thin-walled tubes, which are at 
first very tiny, but after repeated connection with other tubes ultimately unite 
to form large ducts. These lymph ducts are provided, like the veins, with valves. 
The pressure of the blood within the blood vessels continually forces more 

The lymph vessels. The enlargements 
are lymph glands. The arrow indicates 
where most of the lymph returns to the 
circulatory system. 


plasma into the lymph; thus a slow current is maintained from the lymph 
spaces into lymph tubes. On its course the lymph passes through many lymph 
glands. In these glands some impurities appear to be removed and colorless 
corpuscles made. The lymph ultimately passes into a large tube, the thoracic 
(tho-ras'ik) duct, which leads upward near the ventral side of the spinal column, 
and empties into the large subclavian vein in the left side of the neck. Another 
smaller lymph duct enters the right subclavian vein. 

The Lacteals. — We have already found that part of the digested food 
(chiefly sugars, amino-acids, salts, and water) is absorbed directly into the 
blood through the walls of the villi and carried to the liver. Fat, however, is 
passed into the spaces in the central part of the villi, and from there into other 
spaces between the tissues, known as the lacteals. The lacteals carry the fats 
into the blood by way of the thoracic duct. The lacteals and lymph vessels 
thus have in part the same course. It will be thus seen that lymph at different 
parts of its course would have a very different composition. 

The Effect of Exercise on the Circulation. — It is a fact familiar 
to all that the heart beats more violently and quickly when we are 
doing hard work than when we are resting. Count your own pulse 
when sitting quietly, and then again after some brisk exercise in 
the gymnasium. The average heart beat will be raised from about 
72 beats a minute to between 90 and 100 a minute. Exercise in 
moderation is of undoubted value, because it sends more blood to 
parts of the body where increased oxidation is taking place as the 
result of the exercise. The best forms of exercise are those which 
give work to as many muscles as possible — walking, out-of-door 
sports, any exercise that is not violent. Exercise should not be 
attempted immediately after eating, as this causes a withdrawal of 
blood from the digestive tract to the muscles of the body. Neither 
should exercise be continued after becoming tired, as poisons are 
then formed in the muscles, which cause the feeling we call fatigue. 
Overdoing in any sport or game is dangerous. Fatigue is a signal 
to rest. Obey it ! Remember that extra work given to the heart 
by extreme exercise may injure it, causing possible trouble with 
the valves. Older people and those who through excessive use 
of stimulants or tobacco, or through overeating have developed 
arteriosdero' sis or hardening of the arteries need to be especially 
careful. ''A man is as young as his arteries," because the har- 
dening of the wall raises the blood pressure, and if the inelastic 
artery wall breaks, due to overexercise, death may result through 




Treatment of Cuts and Bruises. — Blood which oozes slowly 
from a cut will usually stop flowing by the natural means of the 
formation of a clot. A cut or bruise should, however, be washed 
in a weak solution of lysol or some other antiseptic in order to 
prevent bacteria from obtaining a foothold on the exposed flesh. 
If blood, issuing from a wound, gushes in distinct pulsations, 
we know that an artery has been severed. To prevent the flow 
of blood, a tight bandage known as a tourniquet (toor'ni-ket) must 
be tied between the cut and the heart if possible. A handker- 
chief with a knot placed over 
the artery may be used for 
this purpose. If this does not 
serve, insert a stick in the hand- 
kerchief and twist it so as to 
make the pressure around the 
limb still greater. Thus we 
may close the artery until a 
doctor can come and sew up 
the injured blood vessel. 

The Effect of Alcohol upon 
the Blood. — Alcohol, when 
taken habitually, causes several 
very serious effects upon the 
blood and blood vessels. The 
bodily resistance against dis- 
ease which is brought about 
by the presence of specific '' antibodies " is greatly weakened in 
those who use alcohol to excess. Drinking also has an injurious 
effect upon the colorless corpuscles, as it lowers their ability to 
fight disease germs. Place a drop of alcohol on a slide contain- 
ing active amoebae, if j^ou wish to see the effect on a similar 
type of organism. Alcohol acts on the nerve centers controlling 
the heart and blood vessels. You all know the red face of the 
habitual drinker. Alcohol may even, in cases of long and severe 
drinking, cause changes to take place in the walls of the blood 
vessels which may result in the breaking of the vessel or the forma- 
tion of a blood clot in the vessel. Such an injury in the brain 
causes ap'oplexy and often results in sudden death. 

Stopping flow of blood tiom di artery 
by applying a tight bandage (tourniquet) 
between the cut and the heart. 


Summary. — The blood has been shown to be more than a mix- 
ture of diffusible food substances, although one of its chief functions 
is to carry food to the body cells. In addition the red corpuscles 
exchange oxygen for carbon dioxide with the tissue cells. The 
plasma also carries antibodies, substances which fight disease- 
causing bacteria. In addition some of these antibodies (as the 
opsonins) assist the colorless corpuscles to rid the body of bacteria. 
Perhaps most important of all, the blood carries the regulating 
hormones, manufactured in the endocrine glands, on the presence 
of which the smooth running of our bodily activity depends. 

The heart has been shown to be a double force pump, which 
sends the blood in two circulations through the body. The pul- 
monary circulation carries the blood to and from the lungs ; the 
systemic takes it to and from all other parts of the body. The 
arteries, capillaries, and veins are the connecting tubes through 
which the blood circulates. 

Fluid food and oxygen reach the tissue cells in the lymph which 
bathes them, and wastes, both liquid and gaseous, are taken away 
by the lymph. 

"Problem Questions 

1. Is the blood a tissue ? Why? 

2. What is the function of the red corpuscles ? Of colorless corpuscles ? 

3. What is the composition of plasma? How do you account for this? 

4. How does lymph differ from plasma ? 

5. What is one of the disease-resisting mechanisms of the blood and how 
does it work? 

6. What are hormones ? What do they do ? How do they do it ? 

7. Prove that the heart is a force pump, 

8. Compare the short and long circulations in the body. 

9. How do cells get food and get rid of wastes? How do they "breathe" ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Broadhurst, How We Resist Disease. Lippincott Company. 
Burton-Opitz, Physiology. W. B. Saunders Company. 
Harrow, Glands in Health and Disease. E. P. Button and Company. 
Martin, The Human Body, Advanced Courses. Henry Holt and Company. 
Sharp, Foundation of Health. Lea and Febiger. 


Prot)lems : A study of respiration to find out: 
{a) What changes in the blood and in the air take place within the 

(h) The mechanics of respiration. 
A study of ventilation to discover : 
(a) The reasons for ventilation. 
(6) The best method of ventilation. 
A study of the organs of excretion. 

Laboratory Suggestions 

Demonstration. Comparison of the lungs of the frog with those of a bird or 
a mammal. 

Experiment. The changes taking place in the air in the lungs. 

Experiment. The use of the ribs in breathing. 

Demonstration experiment. What causes the filling of air sacs in the lungs? 

Demonstration or home experiment. How to perform the Schaefer method 
of artificial respiration. 

Demonstration experiment. Best methods of ventilating a room. 

Demonstration. Best methods of dusting and cleaning. 

Demonstration. Beef or sheep's kidney to show its structure. 

Necessity for Respiration. — We have seen that plants and 
animals need oxygen in order that the life processes may go on. 
Food is oxidized to release energy, just as coal is burned to give 
heat to run an engine. As a draft of air is required to make a fire 
under the boiler, so, in the human body, oxygen must be given so 
that food in the tissues may be oxidized to release energy- used in 
work. This oxidation takes place in the cells of the ])ody, be they 
part of a muscle, a gland, or the brain. 

The Organs of Respiration in Man. — We have noted the fact 
that the lungs are the organs which give oxygen to the blood and 
take from it carbon dioxide. Air passes through the nostrils into 
the windpipe. This cartilaginous tube, the top of which may 




easily be felt as the Adam's apple of the throat, divides into two 
bronchi (br6n'k!). The bronchi within the lungs break up into a 
great number of smaller bronchial tubes, which divide somewhat 
like the small branches of a tree. The bronchial tubes are lined 
with ciliated cells, the cilia of which are constantly in motion. 

They lash with a quick stroke 
toward the outer end of the 
tube, that is, toward the mouth. 
Hence any foreign material will 
be raised first by the action of 
the cilia and then by coughing 
or " clearing the throat. '^ The 
bronchial tubes end in very 
minute air sacs, little pouches 
having elastic walls, into which 
air is taken when we inspire, or 
take a deep breath. In the 
walls of these pouches are nu- 
merous capillaries. It is 
through the very thin walls of the 
air sacs that a diffusion of gases 
takes place ivhich results in the 
blood giving up carbon dioxide, 
and taking up oxygen in its 

Changes in the Blood within the Lungs. — Blood leaving the 
lungs is much brighter red than when entering them. The change 
in color is due to the combination of oxygen with the haemoglobin 
of the red corpuscles to form oxyhsemoglobin. The changes 
taking place in the blood are obviously the reverse of those which 
take place in the air in the lungs. 

Changes in Air in the Lungs. — Air is much warmer when it 
leaves the lungs than before it enters them. Breathe on the bulb 
of a thermometer to prove this. Expired air contains a consider- 
able amount of moisture, as may be proved by breathing on a cold 
polished surface. The loss of moisture from the body in expired 
air is about half a pint in twenty-four hours. Carbon dioxide in 
expired air may be detected easily by the lime water test. 

The lungs are two masses of many tubes 
and sacs. 


Composition of Fresh Air and of Air Expired from the Lungs 


In Outdoor Air 

In Air Expired 


Carbon dioxide 

Nitrogen and other gases .... 
Water vapor 



+ .60 

As the table shows, there is a loss of nearly 5 per cent of oxygen, 
and a corresponding gain in carbon dioxide and water vapor, in 
expired air. There are 
also some organic waste 
substances in expired air 
which are not shown in 
the above table. 

Cell Respiration. — It 
has been shown, in the 
case of very simple ani- 
mals, such as the amoeba, 
that when oxidation 
takes place in the cell, 
energy results from this 
oxidation. In man the 
oxygen taken into the 
lungs is not used there, 
but is carried by the 
blood to the digestive 
tract, to the muscles, and 
to all other parts of the 
body where work is done. 
Cell activity demands 
food and oxygen. 

While work is being 
done, certain wastes are 
formed in the cell. Car- 
bon dioxide is given off when carbon is burned. And when pro 
teins are burned, other wastes containing nitrogen are formed 

Exchange of gases through the walls of an air 
sac in the lungs. The diagram shows one air sac 
as if laid open in two parts ; and another air sac, 
below, intact. 



These must be passed off from the cells, as they are poisons. 
This is done by the lymph and the blood, taking the waste materials 

to points where they may 
be excreted or passed out 
of the body. 

The Pleura. — The 
lungs are covered with a 
thin elastic membrane, 
the pleura. This forms 
a bag in which the lungs 
are hung. Between the 
walls of the bag and the 
lungs is a space filled with lymph. By this means the lungs are 
prevented from rubbing against the walls of the chest. 

The Mechanics of Respiration. — In every breath there are two 
movements, inspiration (taking air in) and expiration (forcing air 
out). An inspiration is produced by the contraction of muscles 
between the ribs, together with the contraction of the diaphragm,, 

Respiration of a cell. 

The chest cavity {A) at the time of a full breath : 
{B), after an expiration. Explain how the chest 
cavity is made larger. 

Apparatus to show the me- 
chanics of breathing. 

the muscular wall forming the floor of the chest cavity; this 
results in pulling the diaphragm down and pulling the ribs up- 
ward and outward, thus making the space within the chest cavity 



larger. The lungs, which he within this cavity, are filled by the 
air rushing into the larger space thus made. An expiration is 
simpler than an inspiration, for it requires no muscular effort ; 
the muscles relax, the breastbone and ribs sink into place, while 
the diaphragm retiu'ns to its 
original position and the air is 
pushed out. 

Rate of Breathing and Amount 
of Air Breathed. — During quiet 
breathing, the rate of inspiration is 
from fifteen to eighteen times per 
minute; this rate largely depends 
on the amount of physical work 
performed. About 30 cubic inches 
of air are taken in and expelled 
during the ordinary quiet respira- 
tion. The air so breathed is called 
tidal air. In a " long " breath, we 
take in about 100 cubic inches in 
addition to the tidal air. This is 
called complemental air. By means 
of a forced expiration, it is possible 

to expel from 75 to 100 cubic inches more than tidal aii-; this air is called 
reserve air. What remains in the lungs, amounting to 100 cubic inches, is 
called the residual air. The value of deep breathing is seen by a glance at the 
diagram, for when we take a deep breath we ventilate the lungs and exercise 
the deeper-placed air sacs. 

Hygienic Habits of Breathing. — Every one ought to accustom 
himself upon going into the open air to inspire slowly and deeply 
to the full capacity of the lungs. A slow expiration should follow. 
Take care to force the air out. Breathe through the nose, thus 
warming the inspired air before it enters the lungs. Repeat this 
exercise several times every day. You will thus prevent certain 
of the air sacs which otherwise are not often used from becoming 
hardened and permanently closed. 

Deep breathing should become a habit with growing girls and 
boys. It can best be practiced in your bedroom, with windows 
open, after rising in the morning and just before retiring at night. 

Common Diseases of the Nose and Throat. — Catarrh is a dis- 
ease to which people with sensitive nmcous membrane of the nose 

H. NEW CIV. BIOL. — 13 

Diagram showing the relative amounts 
of tidal, complemental, reserve, and resid- 
ual air in the lung capacity of an adult man. 



and throat are subject. It is indicated by the constant secretion 
of mucus from this membrane. Frequent spraying of the nose 
and throat with some mild antiseptic solutions is found helpful. 
Chronic catarrh should be attended to by a physician. Often we 
find children breathing entirely through the mouth, because the 
air passages in the nose are closed. When this has gone on for 
some time the nose and throat should be examined by a physi- 
cian for ad'enoids, or growths of soft masses of tissue which fill up 


^M& A 




*-'« r 





- : — ' -_ 

■ •'" 

The Schaefer method of artificial respiration. 

the nose cavity, thus causing mouth breathing. Many a child, 
backward at school, thin and irritable, has been changed to a 
healthy, normal, bright scholar by the removal of adenoids. Some- 
times the tonsils at the back of the mouth cavity become diseased 
and enlarged, causing serious- throat troubles and sometimes acute 
rheumatism and heart disease. (See page 151.) 

Suffocation and Artificial Respiration. — Suffocation results 
from shutting off the supply of oxygen from the lungs. It may 
be brought about by an obstruction in the windpipe, by a lack of 
oxygen in the air, due to inhaling some other gas in quantity, by 


drowning, or from a severe electric shock. In any one of the 
above cases, the person's Hfe may be saved by prompt recourse to 
artificial respiration. The Schaefer method is considered the best 
and should be given as follows : Place the patient face downward, 
taking care to keep the mouth and nose free from dirt. Kneel 
astride the patient at his knees and slowly but strongly press 
down and forward with the hands immediately over the lower 
part of the chest cavity, and arms straight. Keep this pressure 
for about three seconds and then swing your body off suddenly, 
thus allowing the lungs to fill with air. After two seconds repeat 
the pressure as before. Count the seconds as you do this so as 
to time the total respiration movements at twelve to a minute. 

Do not give up work if the patient shows no signs of recovery. 
Persons who have been for some time under water have been re- 
suscitated after from four to five hours work. Prompt and regular 
effort is the thing that counts. 

The Need of Fresh Air. — We are all aware of the discomfort 
that comes in the crowded auditorium or schoolroom at the end of 
a school period. Some people think that this discomfort is caused 
by lack of oxygen in the air or by the presence of too much carbon 
dioxide. But experiments conducted by the New York State 
Ventilation Commission and in many laboratories have shown that 
this discomfort comes largely from two sources, the rise in tempera- 
ture and the increase in humidity in the air. The source of this 
heat and moisture is largely the bodies cf the people who are in the 
room. The death of the unfortunates in the " Black Hole of 
Calcutta," which in the past was thought to be due to lack of 
oxygen, was probably caused by heat stroke, due to the increased 
moisture and rise in temperature from so many bodies packed into 
the small room. 

Need of Ventilation. — In order to get rid of excess moisture, 
reduce the heat, and remove the other products of respiration 
from the air, ventilation is necessary. Ventilation is defined as 
adequate replacement of used air with fresh air. In addition, air 
in buildings contains dust, with its load of bacteria, odors of various 
kinds, and sometimes poisonous gases. 

While natural ventilation, or the exchange of inside air and out- 



Natural ventilation. Air finds a way of entrance 
into most of our rooms. 

door air through cracks, window casings, chimney hearths, opening 
doors, etc., is often enough to change the air in rooms not con- 
stantly used, it becomes necessary to use other means in schools 
and other crowded buildings. From 2000 to 3000 cubic feet of air 

is considered as the need 
of the average person 
each hour ; and various 
devices for changing the 
air frequently are in use. 
In schools air is often 
drawn in by fans, washed 
to remove dust and bac- 
teria, and then forced 
through ducts into the 
rooms, the used air pass- 
ing out through other 
ducts. Windows open a 
short distance at top and 
bottom are the best means of ventilation for the house. A board 
should be placed in front of the open space to prevent direct drafts, 
for strong drafts chiU the skin, with a consequent congestion of 
blood vessels and possible cold. 

A temperature of not more than 68° F. is most favorable for 
mental work. It is found that during the winter, when artificial 
heat is used, the air becomes too dry. Various devices, the simplest 
of which are pans of water on registers or radiators, evaporate 
moisture and raise the humidity content of the air somewhat, but 
no effective device is in general use for keeping the humidity 
equal to that of the outside air. Consequently, when we go from a 
warm, dry room into a cool, out-of-door air, the skin becomes 
chilled and we may take cold. 

Ventilation of Sleeping Rooms. — Sleeping in badly ventilated 
rooms is the cause of much discomfort and often of illness. Beds 
should be placed so that a constant supply of fresh air is given 
without a direct draft. This may often be managed with the use 
of screens. Bedroom windows should be kept open for a time in 
the morning to allow free entrance of the sun and air, bedclothes 
should be washed frequently, and sheets and pillow covers often 



changed. Bedroom furniture should be simple, and but little 
drapery should be allowed in the room. Do you know why? 

In cities especially, the 
night air is purer than day 
air, because the factories 
have stopped work, the 
dust has settled, and fewer 
people are on the streets. 
The old myth of " night 
air" being injurious has 
long since been exploded, 
and thousands of people of 
delicate health, especially 
those who have weak 
throats or lungs, are re- 
gaining health by sleeping 
out of doors or with the windows wide open. The only essential 
in sleeping out of doors or in a room with a low temperature is that 
the body be kept warm and the head be protected from strong 

Good window ventilation. The window 
open from both top and bottom. 

Outdoor sleeping places in city and country. 

drafts by a nightcap or hood. Proper ventilation at all times is 
one of the greatest factors in good health. 


Change of Air. — Persons in poor health, especially those having 
tuberculosis, are often said to be cured by '^ a change of air." This 
is probably not so much due to the composition of the air as to 
change of occupation, rest, and good food. Mountain air is dry 
and relativel.y free from dust and bacteria, and often helps a person 
having tuberculosis. Air at the seaside is beneficial for some forms 
of disease, especialh^ hay fever and bone tuberculosis. Many 
sanitariums for this latter disease have been established near the 
ocean, and they have assisted in saving thousands of lives. 

Relation of Proper Exercise to Health. — We are all aware that 
exercise in moderation has a beneficial effect upon the human or- 
ganism. The pale face, drooping shoulders, and narrow chest of 
the boy or girl who takes no regular exercise are too well known. 
Exercise, besides training the muscles, increases the activity of 
the heart and lungs, causing deeper breathing and giving the 
heart muscles increased work; it liberates heat and carbon 
dioxide from the tissues where the work is taking jDlace, thus in- 
creasing the respiration of the tissues themselves, and aids me- 
chanicalh^ in the removal of wastes from tissues. It is well know^n 
that exercise, when taken some little time after eating, has a very 
beneficial effect upon digestion. Exercise and especially games 
are of immense importance to the nervous system as a means of 
rest. The number of playgrounds in this country is increasing, 
because of this acknowledged need of exercise, especially for grow- 
ing children. 

Proper exercise should be moderate and varied. Walking in 
itself is a valuable means of exercising certain muscles, and so is 
swimming, but neither is ideal as the only form to be used. Vary 
your exercise so as to bring different muscles into play, take exer- 
cise that will allow free breathing out of doors if possible, and the 
natural fatigue which follows will lead you to take the rest and sleep 
that every normal body requires. 

Exercise should always be limited by fatigue, which brings with 
it fatigue poisons. This is nature's signal to rest. If one eats 
proper food and breathes fresh air, the fatigue point will be much 
further off than otherwise. One should learn to relax when not 
in activity. Even a small amount of rest, between exertions 
which are very close together, increases greatly the length of time 



one is able to continue those exertions. The habit of lying down 
when tired is a good one. 

The Relation of Clothing to Health. — Clothes, like the covering 
of feathers on birds or fur on mammals, are for protection. They 
may be classed as either good or bad conductors of heat. Good 
heat conductors, such as linen or cotton, allow the temperature out- 
side of them to replace that of the layer of air directly around the 
body, while silk and wool are poor conductors and protect the body 
from a lower temperature outside. Warmth of clothing is largely 
dependent on the amount of air held between its fibers. Cool 
clothes have little air space in the meshes of the cloth, while loosely 
woven underclothes are warmer because they absorb perspiration 
rapidly and dry out quickly. Hence they do not feel cold or 
clammy next the perspiring skin as linen and cotton do. Young 
people can wear linen or cotton underclothes safely all the year 
round if they make proper changes in the weight of their outside 
garments. Older persons, on the other hand, need to wear woolen 
underclothes in the winter because these keep out cold and absorb 
perspiration without chilling the skin. 

It is impossible for us to form proper habits of breathing unless 
clothing is worn loosely over the chest and abdomen. The days of 
tight corsets and lacing seem to be over for girls, but much harm 
is done by tight garters. We should avoid 
tight belts or any tight clothing, as it in- 
terferes with natural circulation. 

Organs of Excretion. — All the life pro- 
cesses which take place in a living thing 
result ultimately, not only in the giving off 
of carbon dioxide, but also in the formation 
of organic wastes within (he body. The 
retention of the wastes which contain nitro- 
gen is harmful to animals. In man, the 
skin and kidneys remove these wastes from 
the body, hence they are called the organs 
of excretion. 

The Kidneys. — The human kidneys are 
situated in the dorsal part of the abdominal cavity in the '' small 
of the back " region. Each is about four inches long, two and one 




Kidneys and bladder ; 
kidney in section. 




Diagram of glomerulus, with 
connected artery, vein, and end 
of tubule. 

half inches wide, and one inch in thickness. Its color is dark red. 
If the structure is examined under the compound microscope, it 
will be seen to be composed of a vast number of tiny branched 

and twisted tubules. The outer end 
of each of these tubules opens into the 
pelvis, the space within the kidney ; the 
inner end forms a tiny closed sac. In 
each sac, the outer wall of the tube has 
grown inward and carried with it a very 
tiny artery. This artery breaks up 
into a mass of capillaries. These capil- 
laries, in turn, unite to form a small vein 
as they leave the little sac. Each of 
these sacs with its blood vessels is called 
a glomer^ulus. 

Wastes given off by the Blood in the 
Kidney. — In the glomeruli the blood 
loses by osmosis, through the very thin walls of the capillaries, first 
a considerable amount of water (amounting to nearly three pints 
daily) ; second, a nitrogenous waste material known as u'rea; 
third, salts and other waste organic substances. 

These waste products, together with the water containing them, 
are known as urine. The total amount of nitrogenous waste leav- 
ing the body each day is about twenty grams. It is passed through 
the ure'ters to the u'rinary bladder; from this reservoir it is passed 
out of the body, through a tube called the ure'thra. After the 
blood has gone through the glomeruli of the kidneys it is purer 
than in any other place in the body, because it has lost much of its 
nitrogenous waste in them and before going to them it gave up 
a large part of its carbon dioxide in the lungs. So dependent is 
the body upon the excretion of its poisonous material that in cases 
where the kidneys do not do their work properly, death may ensue 
within a few hours. One should drink plenty of water between 
meals, since urine normally consists of about 96 per cent water 
and 4 per cent dissolved solids. 

Diet plays a very important part in the care of the kidneys. If 
we overbalance our diet with too much protein food, we throw 
increased work on these organs. The nitrogen in proteins cannot 


be oxidized, so, combined with other elements into urea and other 
wastes, it is ehminated through the kidneys. 

The Skin as an Organ of Excretion. — We have already learned 
that the skin is an organ of protection. Let us now see how it aids 
in excretion. If you examine the 
palm of your hand with a lens, you 
will notice the surface is thrown into 
little ridges. Between these ridges 
may be found a large number of 
very tiny pits ; these are the pores 
or openings of the sweat-secreting 
glands. From each opening a little 
tube penetrates deep within the 
dermis ; there, coiling around upon 
itself several times, it forms a sweat 
gland. Close around this coiled 
tube are found many capillaries. 
From the blood in these capillaries 
cells lining the wall of the gland 
take water, and with it a little car- 
bon dioxide, urea, and some salts 

(common salt among others) . These form the excretion known as 
sweat, or perspiration. The combined secretions from these glands 
amount normally to a little over a pint during twenty-four hours. 
At all times a small amount of sweat is given off, but this is evap- 
orated or is absorbed by the underwear; as this passes off un- 
noticed, it is called insensible perspiration. In hot weather or after 
hard manual labor the amount of perspiration is greatly increased. 

Regulation of the Heat of the Body. — The body temperature of 
a person engaged in manual labor will be found to be but little 
higher than the temperature of the same person at rest. Muscles, 
nearly one half the weight of the body, release about five sixths Oi 
their energy as heat. At all times they are giving up some heat. 
How is it that the body temperature does not vary greatly at 
different times ? The temperature of the body is largely regulated 
by means of the activity of the sweat glands. The blood carries 
much of the heat, liberated in the various parts of the body by 
the oxidation of food, to the surface of the body, where it is lost 

Diagram of sweat gland, duct, 
pore in epidermis. 




in the evaporation of sweat. In hot weather the blood vessels of 
the skin are dilated ; in cold weather they are made smaller by 
the action of the nervous system. The blood thus loses water in 
the skin, and as the water evaporates, we are cooled off. The object 
of increased perspiration, then, is to remove heat from the body. 
With the large amount of blood present in the skin, perspiration is 
increased; with a small amount, it is diminished. Hence, we 
have in the skin an automatic regulator of body temperature. 

Colds and Fevers. — The regulation of blood passing through 
the blood vessels is under control of the nervous system. If this 
mechanism is interfered with in any way, as for example .through 
bacterial toxins released in the body, the sweat glands may not 
do their work, perspiration may be stopped, and the heat from 
oxidation held within the body. The body temperature goes up, 
and a fever results. 

If the blood vessels in the skin are suddenly cooled when full of 
blood, they contract and send the blood elsewhere. As a result a 
congestion may follow. Colds are, in real- 
ity, a congestion of membranes lining cer- 
tain parts of the body, as the nose, throat, 
windpipe, or lungs, together with a growth 
of bacteria which were present in the mouth 
or throat. Some colds are communicable 
and gain entrance to the body when the re- 
sistance is low. 

When suffering from a cold, it is therefore 
important not to chill the skin, as a full 
blood supply should be kept in it and so 
kept from the seat of the congestion. For 
this reason hot baths (which call the blood to the skin) , the avoid- 
ing of drafts (which chill the skin) , and warm clothing are useful 
factors in the care of colds. Very important also are rest in bed, 
fresh air, plenty of water to drink, and free bowel movements. 

Summary. — The organs of respiration, the lungs, are connected 
with the outside air through the bronchial tubes, windpipe, and 
nostrils. Inspiration is brought about by raising the ribs and 
lowering the diaphragm. This makes the chest cavity larger and 
thus allows air to rush into the air sacs. The lungs are the struc- 

Blood vessels : A, normal 
B, congested. 


tures which make possible tissue respiration, by supplying oxygen 
to the blood. The red corpuscles in the lungs lose the carbon 
dioxide that they have taken from the tissues, replacing it with 
oxygen. This is accompanied by a change from dull red (blood 
which is poor in oxygen) to bright red (richlj^ oxygenated blood) . 
Other changes take place in other parts of the body. In the walls of 
the food tube, especially in the small intestine, the blood receives 
its load of fluid food. In the muscles and other working tissues 
the blood gives up food and oxygen, receiving carbon dioxide and 
organic waste in return. In the liver, the blood gives up sugar, 
and the worn-out red corpuscles which break down and are re- 
moved from the circulation. In the glands, the blood gives up 
the materials used by the gland cells in their manufacture of se- 
cretions. In the kidneys, it loses water, urea, and other wastes. 
In the skin, it also loses some waste materials, salts, and water. 

Problem Questions 

1. How are the lungs adapted to do their work? 

2. Explain the mechanics of breathing. 

3. What are the products of respiration ? 

4. Explain the principles underlying the Schaefer method of artificial 

5. What is ventilation? Why is it necessary? 

6. What is cell respiration ? Explain fully. 

7. How does the kidney do its work? 

8. How does the skin excrete wastes? 

9. What is a congestion and how is it caused ? 
10. How do we " take cold" ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 

Fisher and Fisk, How to Live. Funk & Wagnalls Company. 

Harrow, Glands in Health and Disease. E. P. Button and Company. 

Hough and Sedgwick, The Human Mechanism. Ginn and Company. 

McCarthy, Health and Efficiency. Henry Holt and Company. 

Martin, The Human Body, Advanced Course. Henry Holt and Company. 

Sharp, Foundation of Health. Lea and Febiger. 

Woodman and Norton. Air, Water and Food. John Wiley and Sons. 




Problems : What are the chief responses to stimuli in plants and 
animals f 

What are the means for direction and control in plants f 
What are the means for direction and control in simple animals f 
Hovj is man^s body controlled? 
What are the organs of sense in man f 

Laboratory Suggestions 

Demonstration. Review of some tropisms in plants. 

Demonstration. Simple reactions in Paramecium. 

Demonstration. Some types of sensory structures, in insects, crustaceans, 
v/orms, etc. 

Demonstration. The central nervous system of the frog compared with 
models of the central nervous system of man. 

Demonstration. A neuron under the compound microscope. 

Home Laboratory Exercises 

(1) To determine areas of the skin most sensitive to touch. 

(2) To map out hot and cold spots on an area on the wrist. 

(3) To determine the functions of different areas on the tongue. 

Why Plants and Animals respond to Stimuli. — We have 
learned of many instances of response to stimuli. In our experi- 
ments with plants we have found examples of responses to Hght, 
gravity, and moisture. These simple responses are called tropisms. 
But if we are asked to explain why these responses took place, we 
can only say that the protoplasm has exhibited its power of irrita- 
bility, a power by means of which the organism is preserved from 
injuries and by which it obtains from its environment that which 
it needs to carry on its life processes. 



How Plants and Animals receive Stimuli. — In the simplest 
plant and animal cells which live by themselves there are no spe- 
cialized parts which are especially fitted to receive outside stimuli. 
The amoeba, for example, is influenced 
by temperature, food, and other stimuli, 
but it has no sense organs. Some tiny 
plant-like animals (or animal-like plants) 
such as eugle'na have a tiny structure 
called an eyeshot, which seems to be more 
sensitive to light than other parts of the 

The more complex single-celled ani- 
mals, as Paramecium, have parts of the 
cell (cilia) more sensitive to touch than other parts. Animals 
and, to a lesser degree, plants, as they become more complex in 
structure, tend to have special parts set aside to receive stimuli. 
These special parts of complex animals are called sense organs. 

Responses in Plants and Animals. — The tropisms may be listed 
as foUows : 

Euglena. Point out nu- 
cleus, vacuole, chloroplasts, 
and flagellum. The eyespot is 
the dark granular mass above 
the vacuole, near the top. 




' Phototropism or response to light (see page 16) 
Geotropism or response to gravity 
Hydrotropism or response to water 
Thigmotropism or response to contact 
Chemotropism or response to chemical substances 
Thermotropism or response to temperature changes 

^ Galvanotropism or response to electricity 
Rheotropism or response to water currents 
Anemotropism or response to air currents 

The response of roots to gravity, the growth of stems toward the 
source of light, the opening of some flowers in the daytime and 
others only at night, the climbing of plants by means of tendrils or 
other organs stimulated by touch, are a few of the many examples 
which might be mentioned. 

Some Parts of the Plant are More Sensitive. — While a plant 
as a whole is sensitive to stimuli of different kinds, it is certain that 
some parts are more sensitive than others. For example, experi- 
ments show that in the root an area of not more than one milli- 


meter in length is most sensitive to gravity, as the turning response 
takes place there (see page 67). Some tips of stems show a simi- 
lar sensitiveness, as do certain parts of growing leaves. 

The Mechanism of Responses in Plants. — Some of the results 
of these responses are easily seen in plants, but the method by 

which the responses are 
brought about is not so 
easy to see. For example, 
we say leaves place them- 
selves so as to get as much 
hght as possible. But this 
movement is different from 
that found in animals which 
have an internal skeleton 
with muscles attached. The 
changes in position in parts 
'ulvinus of plants are often produced 
by a more rapid growth of 
the cells on one side of a 
structure than on the other, 
this growth having been ex- 
cited by an external stimu- 
lus, such as gravity, water, 
light, or heat. Such are 
the curving movements of roots or stems. The placing of the 
leaves in a horizontal position is brought about by the more rapid 
growth of tissues on one side of the leaf 
stalk than the other. 

Changes in the position of leaves are 
often brought about by special structures 
at the base of the petiole, as may be seen 
in the bean plant. These structures, called 
pulvi'ni (sing, pulmnus), contain thin- 
walled cells filled with water, and the po- 
sition of the leaf depends on the relative 
amount of water in these cells. The more rapid movements 
of the opening and closing of flower petals ; the changes in po- 
sition of leaflets of the pea, clover, alfalfa, oxalis, and other plants 


Pulvinus of a bean plant : A, external view ; 

B, 1 and 2, section seen through a microscope ; 

C, turning leaves upward ; D, turning leaves 
downward. Explain from text. 

Clover leaf : 1, in the morn- 
ing ; 2, at night. 


at night and in the morning ; and the relatively rapid response 
of the leaves of the sensitive plant to outside stimuU are aU 
explained by changes in the water content of cells in pulvini, or by 
rapid and temporary fluctuations in growth on opposite sides of 
the leaves^ or by a combination of both. But other than external 
stimuli influence and modify the growth and actions of plants. 
We know that enzymes play an important part in the storage of 
food in fruits and seeds, and there seem to be evidences of vitamin 
and hormone action as well. It is probable 
that the protoplasm of a plant is under 
much the same control as is the protoplasm 
of an animal. 

Responses in the Simplest Animals. — 
We have already seen that amoebse and 
paramecia seem to respond to the presence 
of food. Examination of a drop of hay in- 
fusion containing paramecia will show many 
collected around masses of food, indicating 
that they are attracted by it. In another 
part of the slide we may find a number of 
the paramecia lying close to the edge of an 
air bubble, with the greatest possible amount 
of their surface exposed to its surface. 
These animals are evidently taking in oxy- 
gen by diffusion. They are carrying on res- 
piration. A careful inspection of the jar 
containing paramecia shows thousands of 
tiny whitish bodies collected near the surface 
of the jar. Some force or forces keep them 
close to the surface. Professor Jennings and 
others have made careful studies of the reactions of paramecia and 
other one-celled animals to various stimuli, and have found that 
in general they react positively toward favorable and negatively 
toward unfavorable conditions in their environment. For example, 
if a slide containing paramecia is heated at one side, the animals 
will back off from the unfavorable stimulus, then shoot forward 
until they encounter the heat, then again back off and repeat the 
operation until they escape from the heated area. 

Trial and error method of 
a Paramecium. 


This method of escape from the unfavorable environment is 
called the method of trial and error. It is an example of the way 
in which some of the lower organisms react to the unfavorable con- 
ditions of their environment. If by such methods they do not 
escape from harmful conditions, they perish. 

Different intensities of hght, different kinds of light, the passage 
of a current of electricity through the water, different chemical 
substances placed in the water, as well as many other factors, cause 
very definite responses on the part of these one-celled organisms. 
The responses in general save the organism from harm, or help it, 
and thus may be said to be adaptive responses. 

Sense Organs and what they do. — Most plants do not react 
quickly to stimuli, because they have no special sense organs. 
Nor has the amoeba any special part of the cell fitted to receive stim- 
uli. But in animals composed of numerous cells, division of labor 

soon appears, and we have organs fitted to 
receive light stimuli (eyes), touch stimuli 
(tactile hairs, etc.), and sound stimuli 
(sensory hairs, tympana of insects, and 
the ears of higher animals). These end 
organs or structures at the outside of the 
Tactile hairs, claw of lob- animal, when put by nerves in communi- 
cation with organs of movement, like 
muscles, bring about reactions to stimuli which result in obtaining 
food, in escaping from enemies, and in many other important 

Some Examples of Sense Organs. — One of the simplest sense 
organs is a sensory hair which contains nerve cells. These cells 
have become modified, so that when they are stimulated they send 
a message inward to another kind of nerve cell in the central part 
of the body. This cell in turn sends a message which stimulates a 
muscle to work, and the animaFs body is moved either away from 
or toward the source of the stimulus. This type of response is 
known as a simple reflex. 

There are many kinds of sensory structures in the lower animals. 
The antennae of insects are for feeling and for receiving odors and, 
in some insects, sound waves. A few insects like the locust have 
tympana, or ears. Some animals use their ears for balancing and 



some for both balancing and hearing. In the shrimp the " ear " 
consists of a tiny pit, the wall of which is lined with sensory hairs. 
In this pit are small grains of sand or other substances, which move 
about as the animal changes its position, and thus assist in making 
the animal aware of its position in space. A German named 
Kreidl (kri'd'l) showed in an experiment that shrimps, after molt- 
ing, place small grains of sand in their stat'ocysts or balancing pits. 
He kept the shrimps in an aquarium containing small particles of 
iron which the shrimps took in place of sand. Using a magnet, 
Kreidl then found that its 

pull affected the shrimps '^''^J'^'"' 

as did the force of gravity 
when sand grains were in 
the statocysts. This 
showed that the stato- 
cysts are balancing or- 

Light-receiving devices 
are of various kinds, from 
the eyespot in euglena 
or small groups of sensory 
cells to the complicated compound eye of insects and the camera- 
like structure of man. 

The Sense Organs of Man. — We have seen that simpler forms 
of life perform certain acts because outside forces acting upon 
them cause them to react to che stimulus from without. All 
many-celled animals, including man, are put in touch with their 
surroundings by what we call the special sense organs. The senses 
of man, besides those we commonly know as those of sight, hearing, 
taste, smell, and touch, are tnose of temperature, pressure, and 
pain. It is obvious that such organs, to be of use, must be at the 
outside of the body. Thus we find eyes and ears in the head, and 
taste cells in the mouth, cells in the nose for smelling, and others in 
the skin which are sensitive to heat or cold, pressure or pain. 

The Nervous System of Man. — But this is not all. Strangely 
enough, we do not see with our eyes or taste with our taste cells. 
These organs receive the stimulations, which are sent inward by 
means of a complicated system of greatly elongated cell structures, 

H. NEW CIV. BIOL. — 14 

Diagram of a simple reflex : the stimulus of a 
burn, through the action of two nerves, causes a 
muscle to contract promptly. 

/ J Dendrites 


and are relayed by other elongated cells, until the sensory message 
reaches an inner station, in the central nervous system. We see 
and hear and smell in our brains. 

In the vertebrate animals, including man, the nervous system 
consists of two divisions. One includes the brain, spinal cord, 
cranial and spinal nerves, which together make up the cer'ehro- 
spi'nal nervous system. The other division is called the autonom'ic 
nervous system and has to do with those bodj^ functions which are 
beyond our control. Small collections of nerve cells, called gan'- 
glia, are found in various parts of the body. 

Neurons. — A neuron, or nerve cell, like other cells in the 
body, is a mass of protoplasm containing a nucleus. But the body 
of the nerve cell is usualh^ rather irregular 
..^'^xeiibody i^ shape, and distinguished from other cells 

.:^^^-^^ b}^ possessing several delicate, branched, 

protoplasmic projections called den'drites. 
One of these processes, the axon, is much 
longer than the others and ends in a muscle 
..^^^^ or in a network of endings around another 

..Proi-ecfire uerve cell. It is not certain that these two 


nerve cells are actually in contact, but a 
stimulus is transmitted from one ceU to the 
other. Such a communication is called a 
synapse (si-napsO- The axon forms the 
J Terminal brar^ches pathway over whlch uervous impulses travel 
^^^^Afwc/e ^^ ^^^ from the nerve centers. 

Diagram of a neuron or A nerve consists of a bundle of tiny 
nerve unit. axons, bound together by connective tissue. 

As a nerve ganglion is a center of activit}^ in the nervous system, 
so a cell bod}^ is a center of activity which may send an impulse 
over this thin strand of protoplasm (the axon) prolonged many 
hundreds of thousands of times the length of the cell body. Some 
neurons in the human body, although visible only under the 
compound microscope, give rise to axons several feet in length. 

Because some bundles of axons originate in organs that receive 
stimulations and send them to the central nervous system, they 
are called sensory nerves. Other axons originate in the central 
nervous system and pass outward in nerves producing movement 




of muscles. These are called motor nerves. Still other neurons 
connect the sensory and motor neurons. These are called asso- 
ciative neurons. 

Reflexes and their Place in Our Lives. — We have seen that 
reflexes play a very important part in the responsive life of simple 
animals. They are equally important in our own lives. The 
involuntary brushing of a fly from the face, or the attempt to 
move away from the source of annoyance when tickled with a 
feather, are examples of reflexes. In a reflex act, a person does 
not think before acting. The nervous impulse comes from the 
outside sensory cells to motor cells in the spinal cord, or in the 
cerebel'lum, the lower part 
of the brain. The mes- 
sage is short-circuited 
back to the surface by 
motor nerves, without 
ever having reached the 
thinking centers. 

The Brain of Man. — 
In man, the central ner- 
vous system consists of a 
hrain and spinal cord in- 
closed in a bony case. 
From the brain, twelve 
pairs of nerves are given off; thirty-one pairs more leave the 
spinal cord. The brain has three divisions. The cer'ebrum makes 
up the largest part. In this respect it differs from the cere- 
brum of the frog and lower vertebrates. It is divided into two 
lobes, the hemispheres, which are connected with each other by a 
broad band of nerve fibers. The outer surface of the cerebrum is 
gray. It is thrown into folds or convolutions which give a large 
surface, the cell bodies of the neurons being found in this part of 
the cerebrum. Holding the cell bodies and fibers in place is a kind 
of connective tissue. The inner part (white in color) is composed 
largely of fibers which pass to other parts of the brain and down 
into the spinal cord. Under the cerebrum lies the little brain, or 
cerebellum. The two sides of the cerebellum are connected by a 
band of nerve fibers which run around into the lower hind brain or 

Diagram of the nerve path of a simple reflex 


medulla. This band of fibers is called the pons. The medulla is, 
in structure, part of the spinal cord, and is made up largely of fibers 
running longitudinally. 


-Olfactory lobe.rrs Olfactory lobe ...,yy Cerebrum 




\ \ Cerebrum, 

IfM Opficlobe. 

KWiJIedulla \^ 


.Spinal cord L..Splndlcord 


...Spinal cord.. 

f^rog Bird Mammal 

Compare the brains of these four animals. 

The Autonomic Nervous System. — Connected with the medulla 
is that part of the nervous apparatus which controls the muscles 
of the digestive tract and blood vessels, some of the secretions, and 
many functions which have to do with life processes in the body. 
This is called the autonomic nervous system. 

Functions of the Parts of the Central Nervous System of the 
Frog. — From careful studies of living frogs, birds, and some mam- 
mals scientists have learned much of what is known of the functions 
of the parts of the central nervous system in man. 

It has been found that if the entire brain of a frog is destroyed 
or separated from the spinal cord, the frog will continue to live. 
It will not move or croak, but if acid is placed upon the skin so as 
to irritate it, the legs make movements to push away and to clean 
off the irritating substance. The spinal cord is thus shown to be 
a center of defensive movements. If the cerebrum is separated 
from the rest of the nervous system, the frog seems to act a little 
differently from the normal animal. It jumps when touched, and 
swims when placed in water. It will croak when stroked, or 
swallow if food is placed in its mouth. But it manifests neither 


hunger nor fear, and is in every sense a machine which will perform 
certain actions after certain stimulations. Its movements are 
automatic. If we watch the movements of a frog which has the 
brain uninjured in any way, we find that it acts spontaneously. It 
tries to escape when caught. It feels hungry and seeks food. It 
acts like a normal individual. 

Functions of the Parts of the Nervous System of Man. — There 
are three types of functions over which the nervous system has 
control. The first are the so-called autonomic activities of the 
body. The heart beats and we breathe when we are asleep as well 
as when we are awake. Our glands secrete and our kidney cells 
excrete, all without any consciousness on our part. Nevertheless 
the nervous system is always in control. 

A second kind of function is the kind of activity which once was 
learned but now has become ^^ second nature " or habitual. If we 
have well-regulated body machines, we get up in the morning, auto- 
matically wash, clean our teeth, dress, go to the toilet, get our 
breakfast, walk to school, even perform such complicated processes 
as that of writing, without thinking about or directing the machine. 
In these respects we have become creatures of habit. Certain acts 
which once we learned consciously, have become automatic. 

Early in our lives we begin to gain a higher control of our body 
activities. We then make conscious choice; we weigh one course 
of action against another and decide which is the best course for 
us to follow — in short, we think. This is the highest tj^e of 
conscious activity. 

Localization of Functions. — In a general way, our central 
nervous system is like that of the frog. The autonomic activities 
are largely controlled outside the brain. The cerebellum largely 
takes care of the habitual reflexes which we learned when growing 
into childhood. The cerebrum has to do with a large number of 
conscious activities. 

A large part of the area of the outer layer of the cerebrum seems 
to be given over to some one of the different functions of speech, 
hearing, sight, touch, and movements of body parts. The move- 
ment of the smallest part of the body appears to have its definite 
localized center in the cerebrum. In addition, certain areas have 
to do with association, memory ; that is, the cells store memories 


of acts and of things. These areas have to do with our voluntary 
actions, for the stored memories are really stored sensory impres- 
sions. Voluntary acts, then, are the cornpletion of reflexes. Even 

Thinking, abstract 
making decisions 

-'Motor area 
Sensory area 

'Thinking, /earning, 


Loealization of functions in the biain. 

reasoning may be explained as the association of concepts, the 
relation of which is not close. Beasoning is perceiving relation- 
ships in seemingly unrelated facts. 

The Sense Organs of Man. Touch, Temperature, Pressure, 
Pain. — In man, the nervous mechanism which receives touch 
stimulations is located in the folds of the dermis or true skin. 
Special nerve endings, called the tactile corpuscles, are found there, 
each inclosed in a sheath or capsule of connective tissue. Inside 
is a complicated nerve ending, from which axons pass inward to 
the central nervous system. The number of tactile corpuscles 
present in a given area of the skin determines the accuracy and 
ease with which objects may be recognized by touch. The feeling 
of temperature, pressure, and pain is determined by different end 
organs in the skin. Two other kinds of nerve endings exist in the 
skin, which give distinct sensations of heat and cold. These nerve 
endings can be located by careful experimentation. There are 
also areas of nerve endings which are sensitive to pressure, and 
still others, most numerous of all, sensitive to pain. 

Taste. — The surface of the tongue is folded into a number of 
little projections known as papiVloe. In the folds between these 
projections, on the top and back part of the tongue, are located 
the organs of taste. These organs are called taste buds. 



Each taste bud consists of a collection of spindle-shaped neu- 
rons, each cell tipped at its outer end with a hairlike projection. 
These cells send fibers inward to other cells, the fibers from which 
ultimately reach the brain. The sensory cells are surrounded by 
a number of protecting cells which are arranged in layers about 
them. Thus the organ in longitudinal section looks somewhat like 
an onion cut lengthwise. 

How we Taste. Four kinds of substances may be distinguished 
by the sense of taste. These are sweet, sour, bitter, and salt: 
Certain taste cells located near the back of the tongue are stimu- 
lated only by a bitter taste. Sweet substances are perceived by 
cells near the tip of the tongue, sour substances along the sides, 
and salt about equally all over the surface. A substance must be 

Tash cells 
Olfactory cells 

To brain ^__ _ 
Nerve endings, of smell, taste, and touch (pressure). 

dissolved in order to be tasted. Taste and smell are often confused 
and many things which we believe we taste are in reality perceived 
by the sense of smell. Such are spicy sauces and flavors of meats 
and vegetables. That we do not taste certain foods is proved by 
closing the eyes, holding the nose, and chewing several different 
substances in succession, such as apple, onion, and raw potato. 

Smell. — The sense of smell is located in the membrane lining 
the upper part of the nose. Here are found a large number of rod- 
shaped cells which are connected with the fore brain by means of 
the olfactory nerve. In order to perceive odors, it is necessary to 
have them diffused in the air ; hence we sniff so as to draw in more 
air over the olfactory cells. 

Hearing. — The organ of hearing is the ear. The outer ear 
consists of a funnel-like organ composed largely of cartilage which 


External ear Middle ear 

Inner ear 
Semicircular canals 

is of use in collecting sound waves, and the auditory canal, which 
is closed at the inner end by a tightly stretched membrane, the 
tympan'ic membrane. The function of the tympanic membrane 
is to receive sound waves or vibrations in the air, which are trans- 
mitted, by the means of a complicated apparatus found in the 
middle ear, to the inner ear. 

Middle Ear. The middle ear in man is a cavity inclosed by the 
temporal bone, and separated from the outer ear by the tj^mpanic 
membrane. A little tube called the Eustachian tube connects the 
inner ear with the mouth cavity. By allowing air to enter from 
the mouth the air pressure is equalized on the tympanic membrane. 
For this reason we open the mouth at the time of a heavy concus- 
sion and thus prevent the rupture of the delicate tympanic 

membrane. Placed di- 
rectly against the tym- 
panic membrane and 
connecting it with an- 
other membrane which 
separates the middle from 
the inner ear, is a chain 
of three tiny bones, the 
smallest of the body. 
They are held in place 
by very small muscles which are delicately adjusted so as to 
tighten or relax the membranes guarding the middle and inner ear. 
The Inner Ear. The inner ear is one of the most complicated, 
as well as one of the most delicate, organs of the body. Deep 
within the temporal bone there are found two parts, one of which 
is called, collectively, the semicircular canals, the other the cochlea 

It has been discovered by experimenting with fish, in which the 
semicircular canal region forms the chief part of the ear, that this 
region has to do with the equilibrium or balancing of the body. 
That part of the ear which receives sound waves is known as the 
cochlea (Lat., snail shell) because of its shape. This complicated 
organ is lined with sensory cells provided with cilia, and its cavity 
is filled with a fluid. It is believed that somewhat as a stone thrown 
into water causes ripples to emanate from the spot where it strikes, 

■Tympanic membran 

Eustachian tub^---^ ' Cochlea 
Diagram of section of the human ear. 



so sound waves are transmitted by means of the fluid fiUing the 
cavity to the sensory cells of the cochlea and thence to the brain 
by means of the auditory nerve. 

The Character of Sound. — When vibrations which are received 
by the ear follow one another at regular intervals, the sound is said 
to be musical. If the vibrations come irregularly, we caU the 
sound a noise. If the vibrations come slowly, the pitch of the 
sound is low; if they come rapidly, the pitch is high. The ear 
is able to perceive as low as thirty vibrations per second and as 
high as almost thirty thousand. 

Seeing. — The organ of vision, the eye, is almost spherical, and 
fits into a socket of bone, the orbit. A stalklike structure, the optic 
nerve, connects the eye with the brain. Free movement is made by 
means of six little muscles which are attached to the outer coat of 
the eyeball, and to the bony wall around the eye. 

The wall of the eyeball is made up of three coats. An outer 
tough white coat, of connective tissue, is called the sclerotic coat. 




^.Openingin Shutter 

yfe ' ' "■ || s 

Diagram of section of the human eye. Compare it with a camera. 

In front, where the eye bulges out a little, this outer coat is replaced 
by a transparent tough layer called the cor'nea. A second coat, 
the choroid (ko'roid) , is supplied with blood vessels and cells which 
contain pigments. The i'ris is part of this coat which we see through 
the cornea as the colored part of the eye. In the center of the iris 
is a small circular hole, the pwpil. The iris is under the control of 
muscles, and may be adjusted to varying amounts of light, the hole 
becoming larger in dim light, and smaller in bright light. The 
mmost layer of the eye is called the ret'ina. This is, perhaps, the 


most delicate layer in the entire body. Despite the fact that the 
retina is less than -^-^ of an inch in thickness, there are several layers 
of cells in its composition. The optic nerve enters the eye from 
behind and spreads out over the surface of the retina. Its finest 
fibers are ultimately connected with numerous elongated cells, 
which are stimulated by light. The retina is dark purple in color, 
this color being due to a layer of cells next to the choroid coat. 
This accounts for the black appearance of the pupil of the eye, 
when we look through it into the darkened space within the eye- 
ball. The retina acts as the sensitized plate in the camera, for on 
it are received the impressions which are transformed and sent to 
the brain and result in sensations of sight. The eye, like the 
camera, has a lens. This lens is formed of transparent, elastic 
material. It is directly behind the iris and is attached to the 
choroid coat by means of delicate ligaments. In front of the lens 
is a small cavity filled with a watery fluid, the a'queous humor, 
while behind it is the main cavity of the eye, filled with a trans- 
parent, almost jelly-like, vifreous humor. The lens itself is elastic. 
This circumstance permits a change of form and, in consequence, 
a change of focus upon the retina of the lens. By means of this 
change in form, or accommodation, we are able to see both near 
and distant objects. 

Summary. — Plants and animals respond to stimuli of the same 
nature : light, heat, gravity, etc. These responses are called 
tropisms. But the mechanism by which the response is brought 
about is not the same. Plants have no sense organs, although 
parts of their bodies are more sensitive to seme kinds of stimuli than 
other parts. Many of their responses are growth responses. 
But nearly all animals have special sense organs and nerves which 
stimulate muscles and thus bring about movement. 

In all but the lowest animals the simple reflex arc is the most 
typical nervous mechanism. In this we have a sensory neuron 
sending its axon back to a motor cell, stimulating it through a 
synapse, thus causing a movement by means of the motor endings 
in the muscle. Thus a reflex action is brought about. 

The vertebrate animals have the most complicated nervous 
system and sense organs. They are provided with a central nervous 
system : brain and spinal cord, protected by bony coverings; — 


the skull and the vertebral column. There are also organs of 
special sense ; touch, heat, cold, pressure, and pain organs being 
found in the skin, olfactory cells in the nose, taste cells in the 
mouth, while the ear and eye furnish examples of most complex 
sense organs. 

Problem Questions 

1. What are some of the simplest provisions for receiving stimuli in plants 
or animals ? 

2. Do plants have any sense organs? Explain. How do plants differ 
from animals in their method of response ? 

3. How do simple animals respond to stimuli? 

4. What is the work of the central nervous system? of the autonomic 
nervous system ? 

5. WTiat are the functions of the cerebrum? the cerebellum? the spinal 

6. What is a neuron? 

7. ^\Tiat is a reflex? Explain fully. 

8. How are habits formed? 

9. T\Tiat are sensations? T\Tiat are sense organs? 
10. How do we taste ? hear ? see ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Atwood, Civic and Economic Biology. P. Blakiston's Son and Company. 
Davison, Human Body and Health. American Book Company. 
Densmore, General Botany. Ginn and Company. 
Gager, Fundamentals of Botany. P. Blakiston's Son and Company. 
Hough and Sedgwick, The Human Mechanism. Ginn and Company. 
Loeb, Forced Movements, Tropisms and Animal Conduct. J. B. Lippincott 

Martin, The Human Body, Advanced Course. Henry Holt and Company. 
Starling, Human Physiology. Lea and Febiger. 


Problems : To learn what instincts are. 

To learn what habits are and how they are formed. 

To learn some rules for hahit forming. 

To know some useful health habits. 

To find out the effect of alcohol on the nervous system. 

Laboeatory Suggestions 

Demonstration. Instinctive acts on the part of a newly hatched chick. 

Class Exercise. To list good and bad habits. 

Demonstration. To show some eye defects and how they are corrected. 

Class Exercise. To sum up the bad effects of alcohol on man. 

The Body a Self-directed Machine. — The body has been 
likened to an engine in that, while burning fuel, or food, it has done 
work. If the comparison is carried further, however, the simile 
ceases ; for the engine is directed from the outside, while the body 
machine is self -directed. 

Moreover, most of the acts we perform during a day's work are 
the results of the automatic working of this body machine. The 
heart pumps; the blood circulates its load of food, oxygen, and 
wastes; the movements of breathing are performed; the thou- 
sand and one complicated acts that go on every day within the 
body are seemingly undirected. But the chemical messengers 
called the hormones, and the autonomic nervous system, at all 
times have these activities under control. 

Instincts. — In many animals certain important activities of 
life are instinctive, that is, they are performed for the first time 
without being learned. A wasp lays its eggs in the body of a 
caterpillar, which it first paralyzes by stinging ; the oriole weaves 
its nest, or the swallow builds its nest of mud.; the trapdoor spider 
makes its tunnel in the ground and tonishes it with a door — 



these and thousands of other examples might be given. The com- 
plicated activities of the pronuha moth (see page 38) can be ex- 
plained only by instinct, and the moth dies without ever seeing 
her offspring. 

Instincts can best be explained, as many workers with insects 
have shown, as a chain of reflex acts. For example, an insect's mak- 
ing a nest, stinging the prey, laying eggs, etc. are a series of in- 
stinctive acts, each one depending upon the one before. If we 
interrupt the sequence, as by removing most of the food supply 
from the nest, or by giving a fly paper soaked in meat juices, 
instead of rotting flesh, in which to lay its eggs, the life cycle is 
ended because the insect cannot modify its actions. As Professor 
Hodge says, a housefly is about as intelligent as a shot rolling down 
a board. Once the chain of instincts is set in motion by some out- 
side stimulus, it continues until the life is perpetuated by egg- 
laying ; thus instincts are, on the whole, beneficial to the race. 

Modification of InvStincts. — Although Fabre (fa'br') found that 
a certain wasp which instinctively drags its grasshopper prey by 
one antenna would not touch its prey if both antennae were cut 
off, yet there are examples of instincts being modified for the 
benefit of the animal. Some insect larvae, if they have consumed 
all of the plant on which instinct teaches them to feed, will eat 
other kinds of leaves and thus save their lives. Fish and frogs 
can be taught to form new associations, for after many errors 
they will learn to avoid obstacles placed between them and their 
food. A dog may refrain from eating a lump of sugar placed on 
his nose until a word is spoken, because he has formed new nerve 
connections which considerably change his natural instincts and 

How Habits are Formed. — Some of our earliest acts are in- 
stinctive. Babies do not have to be taught to suck ; but as they 
grow older they modify their instincts. They learn to take food 
from a bottle and to wait for it. Later on they learn, by a series of 
trials, to stand erect and then to walk. There is a difference be- 
tween the instinct of sucking and the habits which are learned 
later when a new stimulus is substituted for the old one and the 
child takes other food than its mother's milk. A habit might be 
called an acquired reflex act. 


Habit Formation. — One object of education is the training of 
the different areas in the cerebrum to do their work. When we 
learned to write, we exerted conscious effort in order to make the 
letters. Now the act of forming the letters is done without our 
thought. By training, the act has become a habit. The actual 
performance of the action is then taken up by the cerebellum, 
medulla, and spinal ganglia. Thus the thinking portion of the 
brain is relieved of part of its work. 

It is surprising how little real thinking we do during a day, for 
most of our acts are habitual. Habit takes care of our dressing, 
our bathing, our care of the body organs, our methods of eating ; 
even our movements in walking and the kind of hand we write are 
matters of habit formation. We are bundles of habits, be they 
good ones or bad ones. 

Different Kinds of Habits. — Habits are of many kinds. 
They may concern health and well-being, as proper tooth brush- 
ing, attending to the toilet, maintaining a correct posture, and 
hundreds of simple things we do automatically. Some concern our 
dress and our actions in society. We walk or ride or dance or 
skate or drive a car and have learned to do these things auto- 
matically. Our habits of disposition have become a very important 
part of our lives. We may habitually ^' grouch " or be happy, 
sing or cry, be kind or cross; in short, we may make our own 
characters those of saints or of sinners just as we please. And we 
may form our habits of thought, too : concentration or scatter- 
brain methods, ability to think through our problems, or inability 
to do any real thinking — it all depends upon ourselves. 

Habits must be Formed Early. — We have often heard the 
saying, '' You can't teach an old dog new tricks." This is all too 
true of habit forming. We exercise our muscles and they grow 
larger. Not so with our brain cells ; the neurons stop growing 
while we are still of school age, and after that it becomes our busi- 
ness in life to try to educate a few of the 10,000,000 or so that are 
present in our brains. Habit formation is a very necessary part of 
their training. While the nervous system is young the cells are 
plastic, and pathways are easily established between cells. These 
pathways, like a rut in soft mud, become deeper and deeper with 
use. " Practice makes perfect " is a truism, but it illustrates how 


the habit is formed. Fortunate are the boys and guis of the age 
who read this book, for they are able to form good habits easily. 
But a man or woman of middle age has formed habits, and to 
change them and make new ones is very difficult. The nervous 
system is no longer plastic. 

Importance of Forming Right Habits. — Among the habits which 
should be acquired early in life are those of studying properly, of con- 
centrating the mind, of learning self-control, and, above all, of con- 
tentment. Get the most out of the world about you. Remember 
that the immediate effect of the study of some subjects in school may 
not be great, but the cultivation of correct methods of thinking may 
be of the greatest importance later in life. The men and women who 
have learned how to concentrate on a problem, how to weigh all 
sides with unbiased minds, and then to decide on what they believe 
to be right, are the efficient and happy ones of their generation. 

''The hell to be endured hereafter, of which theology tells, is no worse 
than the hell we make for ourselves in this world by habitually fashioning 
our characters in the wrong way. Could the young but reahze how soon 
they will become mere walking bundles of habits, they would give more 
heed to their conduct while in the plastic state. We are spinning our own 
fates, good or evil, and never to be undone. Every smallest stroke 
of virtue or of vice leaves its never-so-little scar. The drunken Rip Van 
Winkle, in Jefferson's play, excuses himself for every fresh dereliction by 
saying, ' I won't count this time ! ' Well ! he may not count it, and a kind 
Heaven may not count it ; but it is being counted none the less. Down among 
his nerve cells and fibers the molecules are counting it, registering and storing 
it up to be used against him when the next temptation comes. Nothing we 
ever do is, in strict scientific literalness, wiped out. Of course this has its good 
side as well as its bad one. As we become permanent drunkards by so many 
separate drinks, so we become saints in the moral, and authorities in the prac- 
tical and scientific, spheres by so many separate acts and hours of work. Let 
no youth have any anxiety about the upshot of his education, whatever 
the line of it may be. If he keep faithfully busy each hour of the working 
day, he may safely leave the final result to itself. He can with perfect certainty 
count on waking up some fine morning, to find himself one of the competent 
ones of his generation, in whatever pursuit he may have singled out." — 
William James, Psychology. 

Some Rules for Forming Good Habits. — Professor Home gives 
several rules for making good or breaking bad habits. They are : 
First, act on every opportunity. Think of the good habits you would 



like to form and then form them. Second, make a strong start 
No half-hearted effort ever was successful in forming a fiabit. 
Third, allow no exception. You cannot establish the new pathway 
in the nervous system, if you, like Rip Van Winkle, " don't count 
this one." Fourth, for the had habit establish a good one. Most of 
us know our own besetting sins. Some of us have far too many. 
Perhaps it is only a little thing such as forgetting some of the 
numerous conventionalities that make up table manners ; it may 
be something far more important, an uncontrolled emotion or feel- 
ing. Anyway, there is some opposite helpful habit you can substi- 
tute in its place. For example, instead of saying sometimes, " That 
noise drives me wild,'' say nothing, but think to yourself, " There's 
no noise that I can't stand when necessary." Fifth, summoning 
all the man within, use effort of will. Happy is the boy or girl 
who has much of that something we call will power. Happy, too, 
are those who have come to look beyond their own personalities 
and who can ask with assurance, " Lead us not into temptation, 
but deliver us from evil." Habits which are rooted when young in 
moral and religious training are those which in later life will do 
more than any others to steer us straight on the course we would 

take through life. 

Health Habits for the Nervous System. 
-— The nerve cells, like all other cells in 
the body, are continually wasting away 
and being rebuilt. Oxidation of food 
material increases when we do mental 
work. The cells of the brain, like muscle 
cells, are not only capable of fatigue, but 
show this in changes of form and of con- 
tents. Food brought to them in the blood, 
plenty of fresh air, and rest at proper 
times, are essential in keeping the nervous 
system in condition. One of the best methods of resting the brain 
cells is a change of occupation. Tennis, golf, baseball, and other 
outdoor sports combine muscular exercise with brain activity of a 
different sort from that of business or school work. 

Necessity of Sleep. — But change of occupation will not rest 
exhausted neiu-ons. For this, sleep is necessary. Especially is 

Effect of fatigue on nerve 
cells, a, healthy brain cell ; 
b, fatigued brain cell. 



sleep an important factor in the health of the nervous system of 
growing children. Ten hours of sleep should be allowed for a child, 
and eight hours for an adult. At this time the brain cells have 
opportunity to rest and store food and energy for their working 

Sleep is one way in which all the cells in the body, and particularly 
those of the nervous system, get their rest. The nervous system, 
by far the most delicate and hardest-worked set of tissues in the 
body, needs rest more than do other tissues, for much of its work 
directing the body ends only with sleep or unconsciousness. The 
afternoon nap, snatched by the brain w^orker, gives him renewed 
energy for his evening's work. It is not hard application to a 
task that wearies the brain ; it is continuous work without rest. 

Health Habits for the Sense Organs. — Overstimulation of any 
of the sense organs is a bad thing. The taste cells may be over- 
stimulated with too much seasoning in food, with tobacco or alco- 
hol. The ear may be ove'^stimulated by loud noises ; the eye by 
too bright light ; the olfactory cells by too heavy odors. 

The most frequent habits of abuse of the eyes are using them in 
a dull or flickering light or in too bright a light with a glare on the 
page, when reading. Light should come over the left shoulder 
We should avoid looking directly into the source of light. 

Look at either of these figures with one eye closed. If part of the Hnes appear 
blurred, you have astigmatism and should consult an oculist. 

The eyes are also subject to infection and injury from dust, cin- 
ders, flying bits of metal, etc. Certain trades in the past have 
taken a high toll of eye injuries, although now workers are protected 
by proper goggles. In case of soreness or irritation place a drop 

H. NEW CrV. BIOL. — 15 

Y F E V 


of a newly prepared weak solution of argyrol in each eye. This 

may prevent serious eye trouble. 

Many eyes are imperfect because the curvature of the lens is not 

normal. Such defects are 
a cause of headaches, and 
should be remedied by an 

How far away can you read these letters? OCulist. 
Measure the distance. Twenty feet is a test n^u^ -n^z^t^ tt-,-u:4. 

for the normal eye. ^^^ ^^^^^ ^ablt. — 

This chapter has had to do 
with habits and is the best place in the book for a discussion of 
the alcohol question. Although prohibition has made it harder 
for people to obtain liquors, many still drink and some seemingly 
cannot help it. Let us see why. 

The first effect of drinking alcoholic liquors is that of exhilaration. 
After the feeling of exhilaration is gone, for this is a temporary 
state, the drinker feels depressed and less able to work than before 
he took the drink. To overcome this feeling, he takes another drink. 
The result is that before long he finds a habit formed from which he 
cannot escape easily. With body and mind weakened, he attempts 
to break off the habit. But meanwhile his will, too, has suffered 
from over-indulgence. He has become a victim of the drink habit ! 

The Economic Effect of Alcoholic Poisoning. — In the struggle 
for existence, it is evident that the man whose intellect is the quick- 
est and keenest, whose judgment is most sound, is the man who is 
most likely to succeed. The paralyzing effect of alcohol upon the 
nerve centers must place the drinker at a disadvantage. In a 
hundred ways, the drinker sooner or later feels the handicap that 
the habit of drink has imposed upon him. Even before the days of 
prohibition, many corporations, notably several of our greatest 
railroads, refused to employ any but abstainers in positions of trust. 
Who knows the number of railway accidents due to the uncertain 
eye of the engineer who mistook some signal, or to the hazy 
inactivity of the brain of the train dispatcher who, because of 
drink, forgot to send some telegram that was to hold the train from 
wreck ? In business and in the professions, the story is the same. 
The abstainer wins out over the drinking man. 

Effect of Alcohol on Ability to do Work. — In Physiological 
Aspects of the Liquor Problem, Professor Hodge, formerly of Clark 



University, describes many of his own experiments showing the 
effect of alcohol on animals He trained four selected puppies to 
retrieve a ball thrown across a gymnasium. To two of the dogs 
he gave food mixed with doses of alcohol, while the others were 
fed normally. The ball was thrown to a distance of a hundred 
feet as rapidly as recovered. This was repeated 100 times each 
clay for 14 successive days. Out of 1400 times the dogs to which 
alcohol had been given brought back the ball only 478 times, while 
the others secured it 922 times. 

Dr. Parkes experimented with two gangs of men, selected to be 
as nearly similar as possible, in mowing. He found that with one 
gang abstaining from alcoholic drinks and the other not, the ab- 
staining gang could accomplish more. On transposing the gangs, 
the same results were repeatedly obtained. Similar results were 
obtained by Professor Aschaffenburg of Heidelberg University, 
who found experimentally that men ^' were able to do 15 per cent 
less work after taking alcohol." 

Many experiments along the same lines have been made. In 
typewriting, in typesetting, in bricklaying, and in the highest 
type of mental work, the result is the same. The quality and 
quantity of work done on days when alcohol is taken are less than 
on days when no alcohol is taken. 

Mod. Tues. Wed. Thur Fri. Sat. Sun. \ 


'^' -«^ 

Ace i den 















'■— -*^^ 











"* •• 




Notice that the curve of efficiency is lowest on Monday and that crimes and 
accidents are most frequent on Sunday and Monday. Account for this. 

The Relation of Alcohol to Efficiency. — We have already seen 
that neither is work done as well nor is as much accomplished by 
drinkers as by non-drinkers. 

Some relation of alcohol to efficiency is shown by the above chart, 


which was made prior to prohibition. During the week the 
curve of working efficiency is highest on Friday and lowest on 
Monday. The number of accidents were also least on Friday 
and greatest on Monday. Lastly the assaults were fewest in 
number on Friday and greatest on Sunday and Monday. The 
moral is plain. Workingmen were apt to spend their week's 
wages freely on Saturday. Much of this went into drink, and 
resulted in crime on Sunday because of the deadened moral and 
mental condition of the drinker, and loss of efficiency on Monday, 
because of the poisonous effects of the drug. 

Since the prohibition law went into effect, welfare organiza- 
tions have reported a great decrease in cases of destitution and 
dependence caused by drink. Workmen to-day are saving their 
wages or investing in radio sets or in automobiles instead of drink. 

This is one of the greatest arguments in favor of prohibition. 
Reports from various sources in this country show that the average 
family is better off to-day than before 1917. 

The Relation of Alcohol to Crime. — A study, made just before 
the eighteenth amendment was passed, of more than 2500 habitual 



10 20 30 40 SO 60 70 80 90 100 

Belgium ^iiPH 1 

England ^^— ^ 1 

France (■■^^^■i 

Germany p^M*^* 1 

United States ^™^^"" 1 

The proportion of crime due to alcohol (1910) is shown in black. 

users of alcohol, showed that over 66 per cent had committed crime. 
Of 23,581 criminals questioned, 20,070 said that alcohol had led 
them to commit crime. 

The Relation of Alcohol to Pauperism. — Studies of certain 
families which have long been a heavy burden on the state show 
that alcohol is at least partly responsible for their condition. 


Alcohol weakens efficiency and moral courage, and thus leads 
to begging, pauperism, petty stealing or worse, and ultimately to 
life in some public institution. In Massachusetts, of 3230 inmates 
of such institutions, 66 per cent were alcoholics. 

The Relation of Alcohol to Heredity. — Perhaps the gravest 
side of the alcohol question is in its relation to heredity. If each 
one of us had only himself to think of, the question of alcohol might 
not be so serious. But drinkers may hand down to their unfortu- 
nate children tendencies toward drink, as well as nervous diseases 
of various sorts ; an alcoholic parent may beget children who are 
epileptic, neurotic, or even insane. 

In the state of New York there were in 1925 about 45,000 insane 
persons in public and private hospitals. It is believed that about 
one fifth of them, or more than 0000 patients, owed their insanity 
to alcohol used either by themselves or by their parents. In the 
asylums of the United States there were then nearly 240,000 insane 
people. Taking the same proportion as before, there were 48,000 
persons in this country whom alcohol had made or had helped to 
make insane. 

Summary. — In this chapter we learn that instincts, which are 
acts performed without any previous learning, may be modified 
through training. Such are habits, which make us slaves or free, 
depending on the kind of, habits that rule our daily lives. We 
have found that most of our daily routine is habit and that 
habits may be learned most easily when we are young. We have 
learned, too, that habits may be formed quickly if one acts on 
every opportunity, makes a strong start, and keeps at it. We 
find that bad habits may be replaced by good ones, and we 
should make every effort of will to make this substitution in our 
daily life. 

The hygiene necessary to keep the nervous system in good 
condition consists of fresh air, good food, elimination of poisons, 
rest, recreation, and sleep. The sense organs must be kept from 
overstimulation and the eyes in particular must be watched for 

The latter part of the chapter sums up the reasons why alcohol 
is a dangerous narcotic habit former, and from the viewpoint of 
human efficiency, why it is dangerous. 


Problem Questions 

1. Why are instincts important in the lives of animals? Give some 
examples of household pets that show how instincts may be modified. 

2. What are habits? How may they be formed? 

3. Make a list of daily habits that are instinctive in origin, 

4. Make a list of habits of mind that you would like to acquire. How 
would you go to work to do this? 

5. Show what habits would result in the protection of your eyes. 

6. Sum up the reasons why alcohol harms a person through its effects on 
the nervous system. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Fabre, The Wonders of Instinct. The Century Company. 

The Gulick Hygiene Series, Control of Body and Mind. Ginn and Company. 

Home, Psychological Principles of Education. The Macmillan Company. 

James, Talks to Teachers. Henry Holt and Company. 

Hough and Sedgwick, The Human Mechanism. Ginn and Company. 

Welch, Physiological Aspects of the Liquor Problem. The Macmillan Company 

Martin, The Human Body, Advanced Course. Henry Holt and Compa,ny. 

Williams, Personal Hygiene Applied. W. B. Saunders Company. 




Problems: What are some methods of asexual reproduction in 
plants and animals f 

How is sexual reproduction in plants brought about? 
What is the result of reproduction in flowering plants f 
What are the methods of reproduction in simple animals ? 
What is a metamorphosis and of what value is it f 
What is the method of development in birds and mammals f 

Labokatory Suggestions 

Demonstration. Cell division. 

Demonstration. Grafting, layering, slipping in plants. The structure of 
bulbs, corms, tubers, rootstocks, etc. P^egeneration in animal forms, if possible. 
Class Exercise. Conjugation in spirogyra. 
Demonstration. Growth of pollen tubes in sugar solutions. 
Demonstration. Development of a simple animal. 
Class Exercise. A study of the metamorphosis of insects. 
Class Exercise. A study of the metamorphosis of a frog. 
Demonstration or Home Project. Development of a chick. 

The Simplest Reproduction. — The simplest plants and animals, 
composed of single cells, grow. But since they take in food and 
oxygen and give off body wastes through their cell membranes and 
walls, the size of the cell body is limited. This is because though 
the volume grows in proportion to the cube of its diameter, the 
surface grows according to the square of its diameter. Two 
bricks cemented together have less surface 
than two separate bricks. Therefore in order 
to live the cell must get more surface. It 
does this by cell division. 

Pleurococcus, a little green plant often found on tree trunks, 
moist rocks, etc., is good to illustrate cell division in a simple 



Pleurococcus. Cell 
division by simple 

plant. Examined under the microscope, specimens may be 
found showing two, three, four, or more cells. In our study of 
the amoeba we found that a single cell forms 
two by division. In this process the nucleus 
divides first, then the cell body begins to split, 
and eventually two cells are formed, each half 
the bulk of the original cell. 

Cell Division results in Growth in Size. — 
Animals and plants grow larger by a multipli- 
cation of the cells, which are cemented together 
to form tissues. The saying " great oaks from 
little acorns grow " illustrates this fact. The 
growth of roots, buds, leaves, and seeds, the 
development of a kitten, and the shooting up of a boy or a girl at 
adolescence are examples of rapid cell division. 

New Plants may be formed by Cell Division. — It is a matter 
of common knowledge that when a chestnut or a poplar tree is 
cut down, young shoots come up from around the cut stem. 
New geranium plants may be grown from " slips " or cuttings 
from the old plant. Sugar cane and the banana plant are propa- 
gated entirely in this way, not from seeds. Grape vines, straw- 
berry plants, and many others take root where the stem comes 
in contact with the soil. Many grasses, like the couch or quick 
grass, become pests because they spread with such rapidity from 
their underground stems. Ferns and other plants have under- 
ground rootstocks which form new shoots 
that become new plants. Tubers, as the 
potato, and bulbs, as the onion or hly, are 
other examples of vegetative growth known 
as vegetative propagation. 

Regeneration. — In certain animals, lost 
parts grow again by cell division. A flat- 
worm may be cut into as many as twenty 
pieces, each one of which will grow into or 
regenerate sl new worm. Earthworms re- 
generate lost segments and starfish lost rays. 

Crustacea regenerate lost antennae or other appendages ; it is com- 
mon for the fiddler crab, when caught, to drop a claw in order to 

Regeneration. A star- 
fish that has lost one of its 
rays will grow a new one. 



Budding and grafting. A, bud; B, stock; 
C, budding completed ; D, two scions in place ; 
E, grafting completed by coating of wax. 

escape from its enemies, and for a new claw to form later on the 
stump of the old one. The common swift, a lizard, will throw off 
its tail to escape being 
caught; a new tail may 
later be regenerated. 

Grafting. — A familiar 
method of multiplying 
desirable varieties of fruit 
trees is by grafting. This 
consists in applying a 
portion of a tree of the 
desired variety (called 
the scion) to another tree of a nearly related kind (called the stock) . 
The two parts must be so placed that there is a connection between 
the tubes in the outer wood and in the bark of each. Why? 
Peach, apricot, apple, and pear trees are often grafted. Another 
similar method is called budding. A bud of the desired tree is 
inserted under the bark of the stock. The branches growing from 
the bud or scion will bear the same variety of fruit as if they had 
remained on the original tree. Grafting and budding^ as we shall 
see later, are widely used by plant breeders to perpetuate desir- 
able kinds of plants. 

Grafting is also practiced in animals. Hydra, worms, insects, 
and frogs all have been used experimentally. Surgeons graft 
skin after a severe burn, or graft glands in sheep, goats, or other 
animals and rarely in man„ In all of these cases the same thing 
takes place as when we cut ourselves and the wound heals ; new 

tissues are formed by 
the growth of cells. 

Vegetative Propa- 
gation and Reproduc- 
tion. — Since all of the 
above methods of 
growth are caused by 
the division of body 
cells, we speak of them 

Grafting. Professor Morgan of Columbia grafted ^g examples of VCgC- 
parts of earthworms and produced: 1, a very long , ^ _ ^ 

worm ; 3, a two-tailed one ; 5, a very sliort one. tative propagation or 



growth. New living organisms, however, are usually formed by 
other methods. If two cells, from two plants or animals of 
different sexes, come together to form a new individual we call this 
a case of sexual reproduction. But if the new organism is formed 
by a cell or cells separating from a single parent to form a new in- 
dividual this is said to be asexual reproduction. 

Asexual Spores. — Asexual reproduction is usually by means of 
the formation of asexual spores. An example of this kind of spore 

formation is seen in the black mold 
of our homes. If a piece of moist 
bread is exposed to the air in the 
schoolroom for a few minutes, 
then covered and kept in a warm 
place, in a day or two a fuzzy 
whitish growth will appear on the 
surface of the bread. This growth 
shortly turns black. If we now 
examine a little piece of the bread 
with a lens or low-powered micro- 
scope, we find a tangled mass of 
threads (the myce'lium) covering 
its surface. From this mass of 
threads project tiny upright stalks 
bearing round black bodies, the 
sporan'gia or fruiting bodies. 
Little rootlike structures known 
as rhi'zoids dip down into the 
bread, and absorb food. The 
sporangia contain many tiny 
bodies called spores which have 
been formed by the division of the 
protoplasm into many separate 
cells. When grown under favor- 
able conditions, the spores will produce more mycelia, which in 
turn bear sporangia. 

Yeasts are another kind of plants that form asexual spores. 
The yeast plant is microscopic in size. It lives in sugary solu- 
tions, such as fruit juices, and multiplies rapidly by an asexual 




Mold reproduces by means of asexual 



process known as budding. In this process a smaller daughter cell 
is cut off from the parent cell. But if unfavorable conditions come, 
each yeast plant divides into four cells, which have thick resistant 
walls. These cells or spores are able to withstand unfavorable con- 
ditions. When favorable conditions of moisture, temperature, 
and food come again, the 
spores will grow and form 

Yeast : A, reproduction by budding ; 
B, formation of spores. 

yeast plants as before. 

Sexual Spores. — In most 
plants which produce spores, 
however, the spores are formed 
in a different way. The com- 
mon pond scum or spirogy'ra, found in freshwater ponds or quiet 
brooks, is an example. The body of this plant is a filament made 
of cylindrical cells. This body grows by ceU division, each cell 
dividing into two new ceUs that look like the original ceU. Thus 
the plant body grows by asexual reproduction. But another 
method of reproduction occurs. Two filaments lie side by side, 
little projections grow out from adjoining cells, these meet, and 
the contents of the cells in one filament 
pass over and mix with the cell contents 
of the other filament. The cells thus 
formed become resting spores (zy'gospores. 
or zy'gotes) . The cells which came together 
to form these spores are called gametes 
(gam'ets; Gr. gamete, wife). This is a 
very simple tj^e of sexual reproduction 
called conjugation. Under favorable con- 
ditions each zygospore can develop into 
a new^ plant. 

• |i» Reproduction in Some Low Plants. — 

^^ Zygospore ^^ other algae we have a step higher in 
^^^^ the development of gametes. In the 

vauche'ria, a branched alga, two struc- 
tures may be produced from the filament. 
One is a sac and contains a large gamete 
The other is tubelike and contains small 
The sperms when 

Two cells 

Conjugation in spirogyra. 

which is called an egg. 

gametes, called sperms, each with two cilia. 


set free appear to be chemically attracted to the egg cells. If 
a sperm (male gamete) fuses with an egg (female gamete) it is said 
to fertilize the egg cell. From the fertilized egg a new plant will 

eventually grow. This 
method of development, 
which is found in all 
higher plants and ani- 
mals, is known as sexual 



Egg nucleus 


Reproduction in vaucheria. 


Reproduction in Flow- 
ering Plants. — Pollen 
grains of various flowers, when seen under the microscope, differ 
greatly in form and appearance. Some are relatively large, some 
small, some rough, others smooth, some spherical, and others 

Pollen grains as seen through the microscope ; note the varying shapes and sizes. 

angular. They all agree, however, in having a thick wall, with a 

thin membrane under it, inclosing a mass of protoplasm. At an 

early stage the pollen grain contains but a single cell and is a 

kind of spore. A little 

later, however, three 

nuclei may be found 

in the protoplasm. 

Hence we know that at 

least three cells exist 

there, two of which are 

sperm cells or male 


Under certain conditions a pollen grain will germinate. This 
growth may be artificially produced by placing pollen grains in 
sugar solutions of different strengths. In the life of a plant it 

Beginning of 
pollen tube — >• 

A developing pollen grain of the pine. 


occurs when the pollen grain of a given flower lights on the sticky- 
surface of the stigma of a flower of the same kind. 

If we cut the pistil of a large flower (as a lily) lengthwise, we 
notice that the style appears to be composed of rather spongy ma- 
terial in the interior ; the ovary is hollow and is seen to contain 
a number of rounded structures which appear to grow out from the 
wall of the ovary. These are the o'vules. The ovules, under 
certain conditions, will be- 

— Pollen grdin on sticky 
-.stigma has developed 
....a pollen tube 

ivhich has groyrn 

down ibe 

style totheoYdry 

come seeds. An explana- 
tion of these conditions 
may be found if we ex- 
amine, under the micro- 
scope, a very thin section 
of a pistil, on which pollen 
has begun to germinate. 
The central part of the 
style is found to be either 
hollow or composed of a 
soft tissue through which 
the pollen tube can easily 
grow. Upon germination, 
the pollen tube, carrying 
the sperm nuclei with it, 
grows downward in the 
spongy center of the style, 
follows the path of least 
resistance to the space 
within the ovary, and there 
enters the ovule. It is be- 
lieved that some chemical influence attracts the pollen tube. One 
of the sperm nuclei penetrates an ovule by making its way through 
a little hole called the mi'cropyle, and then toward an area of pro- 
toplasm known as the em'bryo sac. The embryo sac is an ovoid 
space, microscopic in size, filled with semi-fluid protoplasm con- 
taining several nuclei. (See figure.) One of the nuclei, with 
the protoplasm closely surrounding it, becomes the egg cell or 
female gamete. It is to this cell that one of the sperm nuclei of 
the pollen tube grows, ultimately uniting with it. The union of 

Sperm cell 

Embryo SBC mth 
several nuclei; 
one, the dark, 
is egg cell 

Fertilization of the ovule. 


the sperm nucleus with the nucleus of the egg to form a single cell is 
known di,^ fertilization. This single cell formed by the union of the 
pollen tube sperm cell and the egg cell is now called a fertilized egg 
or zygote and is the beginning of a baby plant, or embryo. 

The primary reason for the existence of a flower is that it may 
produce seeds from which future plants will grow. After fertili- 
zation the ovule grows into a seed which contains the embryo and will 
develop into an adult "plant. 

The second sperm nucleus unites with another nucleus in the 
embryo sac and grows into a food substance called the endosperm, 

which in some plants is a very 


The remains of the 
flower sfalk (peduncle) 


Placenta , the place seeds 
are attached by the 
Funiculus or 
swollen stalk 

A pea,seed,is a developed 

important part of the seed since 
it supplies the growing embryo 
with nourishment. 

A Typical Fruit, the Pea or 
Bean Pod. — ^If a withered flower 
of any one of the pea or bean 
family is examined carefully, it 
will be found that the pistil 
continues to grow after the 
rest of the flower withers. If 
we examine the pistil from such 
a flower, we flnd that it is the 
ovary that has enlarged. The 
space within the ovary has be- 
come nearly filled with a number 
of ovoid bodies, attached along 
one edge of the inner wall. 
These we recognize as the 
young seeds. The pod, which 
is in reality a ripened ovary with other parts of the flower at- 
tached to it, is considered as a fruit. By definition, a fruit is a 
ripened ovary together with any parts of the flower that may be attached 
to it. The chief use of the fruit is to hold and to protect the 
seeds ; it may ultimately assist in distributing them where they 
can reproduce young plants. 

Development of a Simple Animal. — Many-celled animals are 
formed in much the same way as are many-celled seed plants. A 

.The dried style 

The pea pod is a developed ovary with 
other parts of the flower. 



common bath sponge, an earthworm, a fish, or a dog, — each of 
them begins hfe as a fertihzed egg cell. As in the flowering plant, 
this cell was formed by the union of two other cells, a tiny (usu- 
ally motile) cell, the sperm., and a larger one, the egg. After the 
egg is fertilized by a sperm cell, it splits into two, then into four, 
then into eight, then into sixteen cells, and so on. As the number 
of cells increases, a hollow 

ball of cells called the 
hlas'tula is formed; later 
this ball sinks in on one 
side, and a double-walled 
cup of cells, called a gas'- 
trula, results. Practically 
all animals pass through 
the above stages in their 
development from the egg, 
although these stages are 
often not plain to see 
because of the presence of 
food material (yolk) in the 

In an older stage the 
body consists of three 
layers of cells. Those of 
the outside, developed 
from the outer layer of 
the gastrula, are called the 
ec'toderm; this later gives 
rise to the skin, nervous 
system, etc. An inner 

egg of d 
sea urchin 


A hollow 
cells. a 

Eighf cells 


The blast uld 
begins to 
dent and 
form the 

of a 

grows here 

Development of a many-celled animal. This 
. , „ process is called cleavage or segmentation. 

layer, developed from the 

inner layer of the gastrula, is called the en'doderm; this forms the 
lining of the digestive organs, etc. A middle layer, called the 
mes'oderm, lying between the ectoderm and the endoderm, gives 
rise in higher animals, to muscles, the skeleton, and parts of other 
internal structures. 

Asexual Growth. — There are some exceptions to the general 
rule of development of animals stated in the last section. Some 


amoeba-like oi^anisms produce asexual spores ; the malarial para» 
site is a good example. Sponges, the hydra, hydroids, and some 
other animals may produce new forms by budding. In the life 
of the hydroid there is a regular alternation of a period in which 
asexual reproduction takes place (by means of budding off new in- 
dividuals of the colony) with a period in which sexual reproduction 
takes place. In the latter stage eggs and sperms are produced by 
free-swimming jellyfish. This is known as alternation of genera- 
tions. This alternation of a sexual with an asexual generation is 
also plainly seen in many plants, notably mosses and ferns. 

Life History and Metamorphosis. — The period from the time 
the egg is fertilized to the death of the organism is called the life 

history. In many ani- 
mals this life history is 
simple and easy to follow. 
In others it is very com- 
pHcated and frequently 
involves great changes in 
form. For example, a tiny 
flatworm, known as the 
liver fluke of sheep, repro- 
duces within the liver of 
the sheep, on which it is a. 
parasite. The eggs pass 
out with the faeces oi 
the sheep and develop in 
w^ater. If the young fluke 
is so fortunate as to find 
a snail of a certain kind in which it can live at this stage of its 
existence, it enters the snail's body, goes through several changes 
of form there, and eventually gets out of the snail's body, forms 
a hard protective covering or cyst, and attaches itseK to a blade 
of grass. If a sheep happens to eat the grass containing the 
cyst, the parasitic fluke begins a life of activity again, the cyst is 
dissolved by the digestive juices of the sheep, the fluke soon begins' 
laying eggs, and the life cycle is completed. In this life cycle the 
fluke goes through several changes of body form. Such a develop- 
ment is called ^ metamorphosis. 

Stages in the life history of the grasshopper. 
Note the absence of wings in 1 and 2. The adult 
female 4 is lajdng eggs in a hole she has made in 
the ground. 



Life History of the Grasshopper. — The female grasshopper lays 
her eggs in a hole which she has dug in the ground with her ovi- 
positor. From twenty to thirty fertilized eggs are laid in the 
autumn; these hatch out in the spring as tiny wingless grass- 
hoppers. The young molt, or shed their outer covering in order to 
grow larger, each grasshopper 
undergoing about five molts be- 
fore reaching the adult state. 
Since no great change in form 
occurs, the metamorphosis is said 
to be incomplete. In autumn 
most of the adults die, only a few 
surviving the winter. 

Life History of the Cabbage 
Butterfly. — Although a frequent 
visitor of our gardens, the cab- 
bage butterfly is perhaps less 
familiar than the earlier stage in 
which it appears as a green cater- 
pillar which eats the cabbage 

Egg. The eggs are laid in the 
early spring on the leaves of 
young cabbage plants. They are 
small, pale yellow, and delicately 
marked with fine lines. 

Larva. In about a week the 
egg hatches and a tiny caterpillar or larva crawls out. It has a 
long segmented body, three pairs of small true legs on the first 
three segments of the body, and five pairs of prolegs or cater- 
pillar legs farther back, which are of great assistance in holding 
on to a leaf. The mouth is provided with toothed mandibles 
for cutting the leaves. The larva eats ravenously and grows 

Pupa. After two weeks of active life, the pupa, a resting stage, 
is formed. The larva fastens itself to a cabbage leaf, fence rail, 
or some other convenient object, and molts. As the skin sHps 
off, the pupa — in this case called a chrysalis — appears. It 


Life history of the cabbage butterfly : 
1, two eggs, highly magnified, on the 
under surface of a leaf ; 2, larva ; 3, 
chrysalis suspended at two points ; ^, 
adult (male). 


directly into an adult. 

is a small oval object, usually green, but sometimes varying a 
little to harmonize with its surroundings. This stage remains for 
two weeks in summer and longer in cold weather. It then cracks 
open down the back and the adult butterfly, or ima'go, comes out. 
A complete metamorphosis is shown by this insect, which during 
its development passes through four distinct stages — egg, larva, 
pupa, and adult. Most insects show a complete metamorphosis. 
Metamorphosis of the Frog. — Not all vertebrates develop 
The frog, for example, undergoes a meta- 
morphosis. Let us ex- 
amine the development 
of the common leopard 

The eggs of this frog 
are laid in shallow water 
in the early spring. 
Masses of several hun- 
dred, which may be 
found attached to twigs 
or other supports under 
water, are deposited at 
a single laying. Im- 
mediately before leaving 
the body of the female 
they receive a coating 
of jellylike material, 
which swells up after the 
eggs are laid. This helps 
to protect them from 
attacks of fish or other 
animals which might use 
them as food. The up- 
per side of the egg is dark, the light-colored side being weighted down 
with a supply of yolk (food) . The f ertihzed egg soon segments (di- 
vides into many cells), and in a few days, if the weather is warm, it 
has grown into an oblong body which shows the form of a tadpole. 
Presently the tadpole wriggles out of the jellylike case and begins 
life outside the egg. At first it remains attached to some water 

Metamorphosis of a frog. 1 to 7, much enlarged ; 
4, 5, and 7, in section ; 8, tadpole with external gills ; 
9 to 11, tadpole with internal gills. Notice the de- 
velopment of the legs and the disappearance of 
the tail. 


weed by means of a pair of suckerlike projections ; later a mouth 
is formed, and the tadpole begins to feed upon algae and other tiny 
water plants. At this time, about two weeks after the egg was 
laid, gills are present on the outside of the body. Soon after, the 
external gills are replaced by gills which grow out under a fold of 
the skin. Water reaches the gills through the mouth and passes 
out through a hole on the left side of the body. As the tadpole 
grows larger, legs appear, the hind legs first, although for a time 
locomotion is performed by means of the tail. 

Shortly after the legs appear, the gills begin to be absorbed, and 
lungs take their place. At this time the young animal may be 
seen coming to the surface of the water for air. Changes in the 
diet of the animal also occur; the long, coiled intestine is trans- 
formed into a much shorter one. The animal, now insectivorous 
in its diet, becomes provided with tiny teeth and a mobile tongue, 
instead of keeping the horny jaws used in scraping off algae. 
After the tail has been completely absorbed and the legs have 
become full grown, there is no further structural change, and the 
metamorphosis is complete. 

In the leopard frog the change from the egg to adult is completed 
in one summer. In late July or early August, the tadpole begins 
to eat less, the tail becomes smaller (being absorbed into other parts 
of the body) , and before long the transformation from the tadpole 
to the young frog is complete. In the green frog and bullfrog the 
metamorphosis is not completed until the beginning of the second 
summer. The large tadpoles of such frogs bury themselves in 
the soft mud of the pond bottom during the winter. 

Development of Birds. — The white of the hen's egg is put on 
during the passage of the real egg (which is on the yolk or yellow 
portion) to the outside of the body. Before the egg is laid a shell 
is secreted over its surface. If the fertilized egg of a hen is broker 
and carefully examined, on the surface of the yolk will be found 
a little circular disk. This is the beginning of the growth of an 
embryo chick. If the development is followed in a series of eggs 
taken from an incubator at intervals of twenty-four hours or less, 
this spot will be found to increase in size ; and later the little 
embryo will lie on the surface of the yolk. Still later small blood 
vessels can be made out reaching into the yolk for food, and the 


tiny heart can be seen beating as early as the second day of 

incubation. After about three weeks of incubation the httle 

chick hatches and emerges in almost the same form as the adult. 

Development of a 
Mammal. — In most 
mammals after fertili- 
zation the egg under- 
goes development 
within the body of the 
mother. The blood 
vessels, instead of con- 
necting the embryo 
with the yolk as in the 
chick, are attached to 
an absorbing organ, 
known as the jplacen'ta. 
This structure sends 
branchlike processes 
into the wall of the 
u'terus (the organ 

which holds the embryo) and absorbs nourishment and oxygen by 

diffusion from the blood of the mother. After a length of time, 

which varies in different species of mammals (from about three 

weeks in a guinea pig to twenty-two months 

in an elephant), the young animal leaves 

the protecting body of the mother, or is 

born. The young are born in a helpless 

condition, usually, and are nourished by 

milk furnished by the mother until they 

are able to take other food. Thus, higher 

in the scale of life, fewer eggs are formed, 

but those few eggs are more carefully pro- 
tected and cared for by the parents. The 

chances of their growth into adults are 

much greater than when many eggs are 

produced and no care taken of them. 
Summary. — In this chapter we have 

found two general methods of reproduction, 

At the left is an egg, opened to show the embryo 
at the center (the small central spot surrounded by a 
light circle). At the right is an English sparrow one 
day after hatching. Compare this helpless sparrow 
with a newly hatched chick. 

The embryo (e) of a rab- 
bit, and the placenta {v) or 
absorbing organ ; ct, the 
umbilical cord connecting 
the embryo with the pla- 
centa. (After Haeckel.) 


asexual and sexual. The ordinary growth processes of plants 
and animals, those employed by the agriculturist, in slipping, 
layering, budding, and grafting, and the process known as re- 
generation in animals, are examples of growth through cell divi- 
sion and multiplication. Cell division, budding, and the growth 
of spores, are methods of asexual reproduction of animals and 
plants. But another kind of reproduction also takes place. From 
almost the simplest forms of plants and animals to man, sexual 
reproduction is found. In its simplest form it is merely the fusion 
of two cells to form a new cell, which in plants is called a zygote 
and in animals a fertilized egg, and which under favorable condi- 
tions will develop into a complete plant or animal. 

The life history of some organisms is a very simple story indeed ; 
think of pleurococcus. But most plants and animals have com- 
plicated life histories. Some include a change of form or meta- 
morphosis, and some include (as in the liver fluke) parasitism and 
metamorphosis. The higher in the scale of life, the fewer eggs (as 
a rule) are produced and the greater is the protection of the eggs 
and young. In mammals this protection is greatest, for the eggs 
are held in the body of the mother until the embryo is developed 
considerably, when it is born and cared for by the mother. 

Problem Questions 

1. Why do cells have to divide when they reach a certain size? 

2. What kind of development is fission ? Explain. 

3. What kind of development is conjugation? Explain. 

4. Compare asexual and sexual spores in development. 

5. Explain the process of fertilization in flowers. 

6. Compare complete and incomplete metamorphosis. 

7. How might metamorphosis be of value to an animal? 

8. Explain alternation of generations. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Gager, Fundamentals of Botany. P. Blakiston's Son and Company. 
Hegner, Introduction to Zoology. The Macmillan Company. 
Holmes, Biology of the Frog. The Macmillan Company. 
Morgan, Experimental Zoology. The Macmillan Company. 
Needham, General Biology. Comstock Publishing Company. 
Shull, Principles of Animal Biology. McGraw-Hill Book Company. 
Transeau, General Botany. World Book Company. 


Problems : What is meant by a system of classification f 

How are plants classified? 

What is homology f What is analogy f 

How are animals classified f 

Laboratory Suggestions 

A visit to a botanical garden. 

Laboratory exercise. Homologies . and analogies in plants and animals. 

Demonstration. Types which illustrate increasing complexity of body form 
and of division of labor. 

Museum trip. For the identification of examples of the principal animal 
phyla. This should be preceded by objective demonstration work in the 
school laboratory. 

Plants are placed in Groups. — If we plant a number of pea 
seeds so that they will all germinate under the same conditions of 
soil, temperature, and moisture, the seedlings will differ one from 
another in a slight degree. But in a general way they will have 
many characters in common, as the shape of the leaves, the pos- 
session of tendrils, the form of the flower and fruit. A species 
(spe^shez) is the smallest group of plants or animals having certain 
characteristics in common that make them different from all other 
plants or animals. Individuals of a species differ slightly; for 
no two individuals are exactly alike. 

Similar species are placed together in a larger group called a genus 
(je'nus; plu. gen' era). For example, many species of peas — the 
wild beach peas, the sweet peas, and many others — are all grouped 
in one genus (called Lath'yrus, or vetchling) because they have 
certain structural characteristics in common. 

Genera of plants or of animals are brought together in still 
larger groups, the classification being based on general likenesses 
in structure. Such groups are called, as they become successively 



larger, Family, Order, Class, and Phy'lum. In this way both the 
plant and animal kingdoms are grouped into divisions, the smallest 
of which contains individuals very much alike, and the largest of 
which contains very many classes of individuals, each class hav- 
ing some characters in common. This is called a system of 

Classification of Plants. — Four great divisions or phyla of the 
plant kingdom are the Thal'lophytes or thallus plants, those which 
have neither root, stem, or leaves ; the Bry'ophytes or mosses ; the 
Pteridophytes (ter'i-d6-fits) or fern plants; and the Spermat'- 
ophytes or seed-producing plants. Let us begin with the lowest 
forms and briefly examine them, simply with an idea of knowing 
how to distinguish them when we are out in the country or visiting 
a park or a museum. Much pleasure, which is part of the purpose 
of education, may be found in making collections, or at least in 
being able to recognize the differences in the plant and animal 
groups. The pages that follow are incorporated in this biology, 
because the efficient citizen should be well informed along many 
lines. This chapter may make us see the value of museums, bo- 
tanical gardens, and zoological parks. 

I. The simplest plants, called Thallophytes (Lat. thallus, young branch ; Gr, 
phyton, plant), have many forms. They may be single-celled, or many-celled. 
They may or may not have chlorophyll, but they never possess the organs of 
root, stem, and leaves found in the higher plants. Several groups are recog- 
nized. These are the Bacteria, the Fungi, and the Algae. 

Bacteria are discussed in Chapter XXII. 

Tube fungus Sac fungus Basidium fungus 


The Fungi are non-green plants of very great economic importance. There 
are all together about 50,000 species known, and many are widely studied be- 
cause of the harm they do. There are three groups or classes of fungi : 


Class I. The tube fungi (Phycomycetes) , so called because of tbeir tubular bodies. An example 

is bread mold. 
Class II. The sac fungi (Ascomycetes) , which produce spores in an ascus or sac. Examples 

are the yeasts, powdery mildews, and many others. 
Class III. The basid'ium fungi (Basidiomycetes) , so called because their spores are produced 

in a club-shaped structure called a basidium. Mushrooms, puffballs, smuts, and rusts 

belong to this group. 

The Algoe are a very large group of chlorophyll-bearing plants, although 
in some forms the chlorophyll is masked by some other coloring matter. They 
have many forms, ranging from single cells to filamentous colonies or even long 
ribbon or rope-like masses many feet in length as in some seaweeds. They are 
nearly all aquatic. The algae are subdivided as follows : 

(highly magnified) 

Blue green Green 

(highly magnified) 


(ro natural size) 

(235 natural size) 

I. The Di'atoms, one-celled algae having beautifully sculptured cell walls. Many are motile 
and are important sources of food for small fish and other water-living forms. About 12,000 
species are known. 

II. The Blue-green algce contain a blue pigment in the cells in addition to the green color. 
Some common forms are Nostoc and Oscillatoria. About 1200 species have been named. 

III. The Green algce are of countless forms, unicellular, filamentous, plate-like, and in 
irregular masses of cells. There are both fresh -water and salt-water forms, and others live on 
land. The so-called "Red snow" is a form living in snow patches. Pleurococcus and vau- 
cheria are also examples. Some 5000 species have been described. 

IV. The Brown algce are nearly all marine plants. We know them as seaweeds. About 
1000 species are known. 

V. The Red algce, mostly marine, are our most delicate and beautiful seaweeds. There 
are about 3000 named species. 

II. The Bryophytes (Gr. bryon, moss; phyton, plant), consist of two groups 
of plants, the liverworts and the mosses. Both are small plants and nearly all 
live on land. They show a much greater development of tissues than the algae^ 
and may be either thallus-like (liverworts) or have stems with rootlike projec- 
tions and very simple leaves. There are about 16,000 known species. 

in. The Pteridophytes (Gr. pteris, fern), are a group which, when the world 
was younger, played a very important part in the vegetation on the earth. 
Some coal is made very largely from their bodies. They have true roots, 
stems, and leaves, but reproduce like the mosses, by forming spores. . The 
Pteridophytes include three classes, the true ferns, the horsetails (Equisetum), 
and the ly'copods or club mosses. There are about 8000 known species. 



rV. The Spermatophytes (Gr. sperma, seed), or seed-bearing plants, include 

two groups, as follows : 

The Gym'nosperms (Gr. gymnos, naked), or naked-seed-bearing plants, are a 
small group related to the ferns on one side and the flowering plants on the other. 
Two classes are found: the cy'cads, of which the so-called "sago palm " is 
an example, and the co'nifers or evergreens, as pines, spruces, firs, hemlocks, 
cypress, and others. The evergreens include the sequoias, the largest and 
oldest trees. There is a total of only about 450 species of gymnosperms. 

The An'giosperms (Gr. an- 
geion, case or vessel), or true 
flowering plants, are a very 
large group, including all of 
our common grasses and grains, 
our flowering trees and shrubs, 
and flowering plants. There 
are more than 140,000 known 

The total number of known 
species of plants is more than 

Homology and Analogy. 

— In the classification of 
plants and animals, there 
is one underlying principle which is used to show relationships. 
Plants which have similar structures in similar parts of their 
bodies are almost certainly closely related to each other. When 
structures or organs on different animals are found in correspond- 
ing positions and to be similar in structure, they are said to be 
homoVogpus. Homology is of great use in determining rela- 

Angiosperms, or flowering plants : a colony of 
trilliums. (Photograph by W. C. Barbour.) 






Compare the external appearance and the bones of the fore appendage of a bat, 
a bird, a dolphin and a lion. 


tionships in classification. For example, the wing of a bat, the 
wing of a bird, the fore flipper of a dolphin, the fore leg of a lion, 
and the arm of a man are homologous structures and show us 
that these animals come in a rather general relationship. If we 
look further, we find that all have another similar or homologous 
structure called a vertebral column (the '^backbone")- Thus we 
can at once classify these animals as vertebrates. 

Homology often aids us in understanding likenesses in structure 
that are not easily found. It has taken a good deal of study to 
show, for instance, that the paired fins of fishes are homologous 
with the paired appendages of a dog or a cow. But by study- 
ing the development of such structures, the relationship has been 
made clear. 

On the other hand, we often find organs which do not have the 
same structure or origin yet are used for similar purposes. Such 
are the wings of a bird and the wings of a butterfly. Such struc- 
tures are said to be analogous structures. Analogy is likeness in 
function, regardless of origin. 

Classification of Animals. — We have found that a one-celled 
animal can perform certain functions in a very simple way. Man 
can perform these same functions in a very complicated way 
because in him great division of labor is developed and extreme 
complexity of structure is seen. Between these two extremes are 
a great many groups of animals which can be arranged more or 
less as a series. In the pages which follow, the great groups or 
phyla of animals (Protozoa, Porifera, etc.) have been arranged 
beginning with the simplest and ending with the most complex. 

I. Protozo'a (Gr., protos, first; zoon, animal). — Animals composed of a 
cingle cell, reproducing by cell division. About 10,000 species are known. 

Amoeba Monosiga Vorticella 

Protozoa — all highly magnified. 




The following are the principal classes of Protozoa, examples of which we may have seen or 

read about : — 

Class I. Rhizop'oda (root-footed). Having no fixed form, with pseudopodia. Either naked 
as Amoeba or building limy (Foraminifera) or glasslike skeletons (Radiolaria) . 

Class II. Mastigoph'ora. They move by means of long whiplash threads of protoplasm, called 
fiagella. Examples are Euglena and Monosiga. 

Class III. Infuso'ria (in infusions). Usually active ciliated Protozoa. Examples, Parame- 
cium, Vorticella. 

Class IV. Sporozo'a (spore animals). Parasitic and usually non-active. Example, Plas- 
modium malarioe. 

II. Porif' era (Lat. porus, pore ; ferre, bear) or Sponges. — The body con- 
tains many pores through which water bearing food particles enters. They 
are classed according to the skeletons they possess into limy, glasslike, and 


Venus's flower basket 

Bath sponge 

horny fiber sponges. The last named are the sponges of commerce. Most 
sponges live in salt water; they are never free swimming. There are about 
2500 species named. 

The Grantia seen along our northeastern 

The following is their classification : — 
Class I. Calca'rea, having limy spicules in the body. 

coast is an example. 
Class II. Hexactinel'lida. Sponges having glasslike spicules, arranged on three axes. 

pie, Venus's flower basket. 
Class III. Demospon'gice. Sponges with glasslike spicules, not arranged on three axes, or 

with skeleton of horny fiber, the latter type represented by the bath sponge. 

III. Coelentera'ta (Gr. koilos, hollow; enteron, intestine). — The hydra 
and its salt-water allies, the jellyfish, hydroids, and corals, belong to this 
group. They are animals in which the real body cavity is lacking, the simplest 
ones being little more than bags. They have only two cell layers in the body 
wall. These animals are provided with peculiar cells called " nettling cells," by 
means of which they defend themselves from attack and kill their prey. There 
are about 4500 known species. 

There are three classes of the Coelenterata, or Coelen'terates. 

Class I. Hydrozo'a. Simple animals as hydra, or colonial in habit as the hydroids. They 
produce new individuals by budding, and the eggs and sperms are usually produced in a free- 
swimming jellyfish, which buds off from the original colony. This is an example of alterna- 
tion of generations. Examples : Hydra, Obe'lia, and many other hydroids. 

Class II. Scjjx>ho?f/a. Marine jellyfish, mostly of large size. 'Example, Aurelia. 


Class III. Anthozo'a. Hydra-like animals, usually attached, with many tentacles, disposed 
in circlets in multiples of five. They may be single or colonial. The sea anemones and 
corals (which form a skeleton usually of a living substance) are the best known examples. 

Ctenophora (te-n6f'o-ra), or sea walnuts, well known along our eastern coast, are sometimes 
given as a separate phylum and sometimes as a class of the coelenterates. 



Sea anemone 

IV. Platyhelmin'thes (Gr. platys, flat; helminthos, worm), or flatworms. — 
These are usually small, ribbon- or leaf -like and flat, and live in water. Most 
flatworms are parasitic, examples being the tapeworm and liver fluke. There 
are about 5000 known species. 

V. Nemathelmin'thes (Gr. nematos, a thread), or roundworms. — Three- 
layered, elongated threadlike animals, often parasitic. Vinegar eels, the horse- 
hair worm, the pork worm or trichina, and the dread hook- 
worm are examples. About 15,000 species are known. 

Tapeworm. The 
head (h) is shown 
greatly magnified at 


Sandwormi Leech 


There are several classes of these worms and also at least four other phyla of small wormlike 
creatures which it is not the province of an elementary book like this to describe. There are 
perhaps 19,000 described species in these groups. If you are interested in knowing more about 
their structure and names, look up a good book on classification, such as Parker and Haswell's 



VI. Annula'ta (Lat. annulus, a ring), or Coelhelmin'thes. — Segmented 
worms; long, jointed creatures composed of body rings or segments. The 

digestive tract is a tube within a tubelike body, 
pendages. There are about 4000 known species. 

They have no jointed ap- 

There are two classes : 

Class I. Choetop'oda. Many bristles along the sides of the body. Examples are the earth- 
worm or sandworm. 

Class II. Hirudin' ea. Without bristles and having suckers at both ends of the body. Exam- 
ples are the leeches or bloodsuckers. 

VII. Echinoderma'ta. — These are spiny-skinned animals which live in 
salt water. They are more complicated in structure than the worms and may 
be known by the spines in their skin. They show radial symmetry. There 
are about 4500 named species. 

Starfish Brittle star Sea urchin Sea cucumber 


Sea lily 

Classification is as follows : 
Class I. Asteroi'dea, or starfishes. 

Class II. Ophiuroi'dea, the brittle stars or snake stars. 
Class III. Echinoi'dea, or sea urchins. 
Class IV. Holothuroi'dea, including the sea cucvimbera. 
Class V. Crinoi'dea, or stonelike, deep-sea forms, now almost extinct ; sea lilies and sea 


VIII. Arthrop'oda (Gr. arthros, joint; pous, foot). — Animals which are 
jointed, with limy or chitinous exoskeletons and jointed appendages. They 
live in water, or on land, or in the air, or in all three elements. Most of them 
undergo a metamorphosis. There are about 500,000 known species, more than 
all the rest of the animal kingdom put together. 







Class I. Crusta'cea. They live mostly in the water and breathe by means of gills. The head 
and thorax are fused into a hard covering. They have a "crusty" exoskeleton, strength- 
ened with lime. Examples : crabs and lobsters. 
Cl.\ss II. Myriap'oda (thousand legs). They have long bodies with many segments and 

many paired jointed appendages. Centipedes and millepedes are examples. 
Class III. Insec'ta. The largest of all classes of animals (over 450,000 species). Body seg- 
mented ; three regions : head, thorax, and abdomen. Three pairs of jointed legs. Usually 
compound eyes. Breathe through tracheae or air tubes. There are 20 orders, but usually 
examples of only the following eleven orders are found. 
Order 1. Ap'tera (without wings). Very simple insects without wings; with biting mouth 
parts. Examples, springtails and "silver fish" or fish moths, which are found frequently 
in houses. 
Order 2. Ephemer'ida. Insects having complete metamorphosis and biting mouth parts. 
They have long setae which project from the end of the abdomen. The adult lives only 
a day or two, lays eggs, and dies. The mayflies. 
Order 3. Odon'ata. Complete metamorphosis. Biting mouth parts. Adults are expert 

flyers, have large eyes, live mostly in water. Dragon flies and damsel flies. 
Order 4. Or</iop'iera (straight wings). Four wings, front pair straight and leathery. Biting 

mouth parts. Grasshoppers, crickets, cockroaches, walking sticks, etc. (Page 27.) 
Order 5. Coleop'tera (sheath wings). Hard outer wings, forming cover for under wings. 
Biting mouth parts. Complete metamorphosis. All beetles, "June bug," firefly, etc. 
Order 6. H emip'ter a (hali wings). Sucking mouth parts. Complete metamorphosis. Two 

pairs of wings or none. True "bugs, "squash bug, plant lice, scales, cicada. 
Order 7. Neurop'tera (veined wings). Four membranous wings with many veins. Biting 

mouth parts. Complete metamorphosis. Ant lions, dobson fly, etc. 
Order 8. Dip'tera (two wings). Insects with two wings, a few with none. Mouth parts 
fitted for sucking or piercing. Complete metamorphosis. All flies, mosquitoes, gnats, etc. 
There are 40,000 described species and it is estimated that there are more than 300,000 
as yet undescribed. 
Order 9. Siphonap'tera (tube; wingless). Largely parasitic. Sucking mouth. Wings if 

present much reduced in size. Complete metamorphosis. Fleas. 
Order 10. Hymenop'tera (membrane wings). Four membranous wings. Mouth parts 
fitted for biting and sucking. Often long ovipositor modified into sting. Complete 
metamorphosis. Bees, ants, and wasps, gall and ichneumon flies. (Page 26.) 
Order 11. Lepidop'tera (scale wings). Four wings, covered with scales. Mouth parts 
long sucking tube. Complete metamorphosis. Moths and butterflies. 
Class IV. Arachnida (a-rak'ni-da) . This group has no antennse, four pairs of legs, and a 
pair of claw-like appendages on each side of the mouth. Head and thorax combined as in 
Crustacea. The spiders, "daddy-long-legs," scorpions, mites, and ticks are in this class. 

IX. MoUus'ca (Lat. mollis, soft). — These are soft-bodied animals, often 
provided with a shell, which is secreted by a part of the body called the mantle. 
They usually have a single muscular foot on the ventral side. Over 60,000 
species are known. There are three classes. 






Class I. Gastrop'oda (belly-footed). With or without shells, which are usually of one piece 

and coiled. Snail, whelk, slug. 
Class II. Pelecyp'oda (hatchet-footed). Shells of two valves or parts. Clams, oysters, 

scallops, mussels, etc. 
Class III. Cephalop'oda (head-footed). Foot partly surrounds head and bears tentacles or 

grasping organs. Squid, octopus, cuttlefish, etc. 

X. Vertebra'ta. — All the animals we have studied thus far 
agree in having whatever skeleton or hard parts they possess on 
the outside of the body. Collectively, they are called Inver'te- 
brates. In the higher animals called Ver'tebrates, the main or 
axial skeleton is inside of the body. The exoskeleton of inverte- 
brates is dead, being secreted by the cells within, while the endo- 
skeleton of vertebrates is, in part at least, alive and is capable of 
growth; for example, 
a broken arm or leg 
bone will grow to- 
gether. In man, cer- 
tain parts of the skele- 
ton, as nails or hair, 
are formed by the skin, 
and in addition, he 
possesses inside bones 
to which the muscles 
are attached. Some of 
these bones are ar- 
ranged in a flexible 

column in the dorsal (the back) part of the body. This vertebral 
column, as it is called, is distinctive of all vertebrates. Within 
the bony protection of this column lies the delicate spinal cord, 
and to it are attached the big bones of the legs and arms. 
The vertebrate animals deserve more of our attention than other 
forms of life because man himself is a vertebrate. There are 
37,000 known species of vertebrates. 

There are five groups or classes of vertebrates : Pisces, or Fishes ; Amphib'ia, 
or Amphibians ; i^ep^i^m, or Reptiles ; A 'yes, or Birds; Mamma 'Zia, or Mam- 
mals. Let us see how to distinguish one class from another. 

Fishes. — Fishes are familiar animals to most of us. We know that they 
live in the water, and that they have a backbone and fins. The paired fins are 
four in number and correspond in position and structure with the paired limbs 
of man. They are called pectoral and pelvic fins, because they are attached to 

Skeleton of a dog a typical vertebrate. 


the bones forming the pectoral and pehdc girdles. The dorsal, anal, and caudal 
fins are not paired. 

The flattened, muscular body of the fish, tapering toward the caudal fin, 
is moved from side to side with an undulating motion which results in the 

Dorsdl fin. often two 
not pa/red 

paired PecforaJ finr. 
^ paired 

Fins of a fish. 


rapid forward movement of the fish. It also moves slowly by means of the 
paired fins. 

A fish, when swimming quietly or when at rest, seems to be biting even if no 
food is present. Water enters the mouth at each of these biting movements 
and passes out through two slits found on each side of the head of the fish. 
Investigation shows us that under the broad, flat plate, or oper'cuLum, covering 

these slits on each side, lie several long, 
feathery, red structures, the gills. The foun- 
dation of the gill, or the gill arch, is made of sev- 
eral pieces of bone which are held together in 
such a way as to give great flexibihty. Cover- 
ing the bony framework and extending from 
it are numerous delicate filaments covered 
with a very thin membrane. In each of these 
fiilaments are two blood vessels ; in one blood 
flows downward and in the other upward. 
Blood reaches the gills and is carried away 
from these organs b}" means of large vessels 
which pass along the bony arch previously 
mentioned. An exchange of gases through 
the walls of the gill filaments results in a loss 
of carbon dioxide and a gain of oxygen by the 

The gill arches are guarded on the inner side by a series of sharp-pointed 
structures, the gill rakers. Teeth, when present, are used to seize and hold 
prey. In some fishes in which the teeth are not well developed, there seems 
to be a greater development of the gill rakers, in which case they are used to 
strain out food or small organisms from the water which passes over the gills. 
The gullet leads directly into a baglike stomach. There are no salivary 
glands in fishes. There is, however, a large liver, which in some fishes appears 

"^ Diagram of the gills of a fish. 
The heart {H) forces the blood 
into tubes {V) which run out into 
the gill filaments. A gill bar 
(G) supports each gill. Trace 
the course of blood and decide 
what happens in this gill region. 



to be used as a digestive gland. Many fishes have outgrowths, like a series 
of pockets, from the intestine, called the pyloric cceca, which aid in digestion. 
The intestine ends at the vent, which is usually located on the under side of 
the fish, immediately in front of the anal fin. 

An organ of unusual significance, called the swim bladder, occupies the region 
just dorsal to the food tube. The size of the swim bladder can be changed by 
contraction or expansion of its walls. The fish uses this organ to make changes 
in the space it occupies, so that the 
water displaced will equal its own 
weight. Thus the weight of the fish 
is supported no matter at what depth 
it wishes to remain. In some fishes 
(the dipnoi, page 246) it is used as a 

In the fishes the heart is a 
two-chambered muscular organ, a 
thin-walled au'ride, the receiving 
chamber, leading into a thick-walled 
muscular ven'tride from which the 

blood is forced out. The blood is pumped from the heart to the gills ; there 
it loses carbon dioxide and receives oxygen ; it then passes on to other parts 
of the body until it reaches very tiny tubes called cap'illaries. From the 
capillaries the blood returns, in tubes of gradually increasing diameter, toward 
the heart again. (See figure, page 171.) Blood supplies the body cells with 
food and oxygen and carries away wastes. During its course around the 
body some of the blood passes through the kidneys and is there relieved 
of nitrogenous waste. 

As in all vertebrate animals, the central nervous system of the fish consists 
of a brain and a spinal cord; and there are spinal nerves and other nerves. 

The true skeleton, or endoskeleton, is under the skin, as in all vertebrates. I* 
consists of a skull, the vertebral column, which protects the spinal cord, the ribs, 
and other spiny bones to which the unpaired fins are attached. In most fishes 
the exoskeleton, too, is well developed, consisting usually of scales, but some- 
times of bony plates. The skin secretes mucus, a slimy substance which helps 
the fish to go through the water easily. 

Most fishes lay very many eggs. There are about 15,000 species. 

A fish opened to show H, the heart; 
G, the gills ; L, the liver ; S, the stomach ; 
I, the intestine ; O, the ovary ; K, the 
kidney ; B, the swim bladder. 

Elasmobranch Ganoid 



H. NEW CIV. BIOL. — 17 



Classification of Fishes 

Ordeb 1. Elasmohranfchii. Fishes which have a soft skeleton made of cartilage, and ex- 
posed gill slits. Examples : sharks, skates, and rays. 

Order 2. Ganoi'dei. Fishes which once were very numerous on the earth, but which are 
now almost extinct. They are protected by platelike scales. Examples : gars, sturgeon, 
and bowfin. 

Order 3. Teleos'tei, or Bony Fishes. They compose 95 per cent of all living fishes. In this 
group the skeleton is bony, the gills are protected by an operculum, and the eggs are 
numerous. Most of our common food fishes belong to this class. 

Order 4. Dipnoi, or Lung Fishes. This is a very small group. In many respects they are 
more like amphibians than fishes, the swim bladder being used as a lung. They live in 
tropical Africa, South America, and Australia, inhabiting the rivers and lakes there. 

Amphibia. — The frog (page 230) belongs to the class of vertebrates known 
as Amphibia. As the name indicates (amphi, both, and hios, life), members of 
this group live during their life history both in water and on land. In the earlier 
stages of their development they take oxygen into the blood by means of gills. 
When adult, however, they breathe by means of lungs. At all times, but 
especially during the winter, the skin serves as a breathing organ. The skin 
is soft and unprotected by bony plates or scales. The heart has three cham- 
bers: two auricles and one ventricle. (See figure, page 171.) Most amphib- 
ians undergo a metamorphosis, or change of form, the young being unlike 
the adults. About 1500 species are named. 

Classification of Amphibia 

Order 1. Urode'la. Amphibia having poorly developed appendages. Tail persistent 

through life. Examples : mud puppy, newt, salamander. 
Order 2. Anu'ra. Tail-less Amphibia, which undergo a metamorphosis, breathing by gills 

in larval state, by lungs in adult state. Examples : toad and frog. 

Reptiles. — These animals are characterized by having scales developed 
from the skin. In the turtle they have become bony and are connected with 
the internal skeleton. Reptiles always breathe by means of lungs, differing 





in this respect from the amphibians. They show their distant relationship to 
birds in that their large eggs are incased in a leathery, limy shell. There are 
about 1500 known species. 



Classification op Reptiles 

Oeder 1. Chelo'nia (turtles and tortoises). Flattened reptiles with body inclosed in bony 
case. No teeth or sternum (breastbone). Examples: snapping turtle, box tortoise. 

Order 2. Lacertil'ia (lizards). Body covered with scales, usrally having two-paired appen- 
dages. Examples : fence lizard, horned toad. 

Orders. Ophid'ia (snakes). Body elongated, covered with scales. No limbs present. 
Examples: garter snake, rattlesnake. 

Order 4. Crocodil'ia. Fresh-water reptiles with elongated body and bony scales on skin . 
Two-paired limbs. Examples: alligator, crocodile. 

Birds. — Birds are distinguished from all other animals by their covering 
of feathers, which are developed from the skin. These aid in flight and protect 
the body from the cold. 

Bills and feet of various birds : 1, ostrich ; 2, sparrow ; 3, hen ; 4, eagle ; 5, heron 
6, gull ; 7, pigeon ; 8, woodpecker ; 9, parrot ; 10, kingfisher. 

The form of the bill shows adaptations to a wonderful degree. A duck has 
a flat bill for pushing through mud and straining out food ; a bird of prey has a 
curved or hooked beak for tearing ; the woodpecker has a sharp, straight bill 
for piercing the bark of trees mEHEAo 

in search of insect larvae 
which are hidden underneath. 
Birds do not have teeth. 

The rate of respiration and 
of heartbeat and the body 
temperature are higher in the 
bird than in man. Man, 
according to age and other 
conditions, breathes from fif- 
teen to twenty times a min- 
ute. Birds breathe from 
twenty to sixty times a min- 
ute. Because of the increased 
activity of a bird, there comes a necessity for a greater supply of oxygen, an 
increased blood supply to carry the material to be used in the release of 
energy, and a means of rapid excretion of the wastes resulting from the 
process of oxidation. Birds are large eaters, and the digestive tract is fitted 
to digest the food quickly. As soon as the food is part of the blood, it may be 
sent rapidly to the places where it is needed, by means of the strong four- 
chambered heart and large blood vessels. 

Diagram of a bird, showing names of various 


The high temperature of the bird is a direct result of this rapid oxidation ; 
furthermore, the feathers and the oily skin form an insulation which does not 

readily permit the escape of 
heat. This insulating cover is 
of much use to the bird in its 
flights at high altitudes, where 
the temperature is often very 
low. Birds lay eggs and usually 
care for their young. Over 
13,000 species are named. 



Classification of Birds 

Some of the internal organs of a bird. 

Divers and swimmers. Legs short, toes webbed. Examples: 

Like Gallinse, but with weaker legs. Examples : dove, pigeon. 


Obder 1. Rati' toe. Running birds 
with no keeled breastbone. Ex- 
amples : ostrich, cassowary. 
Order 2. Pas'seres. Perching birds ; 
having three toes in front, one be- 
hind. Over one half of all species 
of birds are included in this order. 
Examples : sparrow, thrush, swal- 
Order 3. Galli'noe. Strong legs ; feet adapted to scratching. Beak stout. Examples : 

jimgle fowl, grouse, quail, domestic fowl. 
Order 4. Rapto'res. Birds of prey. Hooked beak. Strong claws. Examples : eagle, 

hawk, owl. 
Order 6. Natato'res. 

duck, albatross. 
Order 7. Colum'boe. 
Order 8. Pica'rioe. 

Two toes point forward, two back- 
ward, an adaptation for climbing. 
Long, strong bill. 
Order 9. Psittaci (sit'a-si). Parrots. 

Hooked beak and fleshy tongue. 
Order 10. Coccyges (kok-si'jez). 
Climbing birds, with powerful 
beaks. Examples : kingfisher, tou- 
can, and cuckoo. 
Order 11. Macrochires (mak-ro-ki'- 
rez). Birds having long, pointed 
wings, without scales on meta- 
tarsus. Examples : swift, hum- 
ming bird, and goatsucker. 
Less common orders are not included 

Mammals. — Dogs and cats, The bison, a grass-eating mammal, 

sheep and pigs, horses and cows, 

all of our domestic animals (and man himself) have characters of structure 
which cause them to be classed as mammals. Mammals, like some other 
vertebrates, have lungs and warm blood. Unlike all other vertebrates they 
have a hairy covering ; nearly all bear young developed to a form similar to 



their own ; ^ and they nurse their young with milk secreted by glands known as 
the mammary glands; hence the term "mammal." 

Of the 3500 species, most inhabit continents ; a few species are found on 

inhabit the ocean. They vary in size from 
tiny shrew mice and moles. Adaptations 

Sea lion, a mammal adapted to life in the sea. 

islands, and some, as the whale, 
the whale and the elephant to 
abound: the seal, the sea lion, 
and the whale have limbs modi- 
fied into flippers ; the sloth and 
squirrel have limbs peculiarly 
adapted to climbing ; while the 
bats have the fore limbs modi- 
fied for flight. 

The lowest mammals are the 
monotremes. Although they are 
provided with hairy covering 
like other mammals, they lay 
eggs like the birds. Such are 
the Australian spiny anteater 
and the duck mole. 

All other mammals bring forth their young alive. The kangaroo and opos- 
sum, however, are provided with a pouch on the under side of the body, in 
which the very immature, blind, and helpless young are nourished until they are 
able to care for themselves. These pouched animals are called marsupials. 

The other mammals may be briefly classified as f ollov/s : — 

Classification of Highee Mammals 

Order 1. Edenta'ta. Toothless or with very simple teeth. Examples: anteater, sloth, 

Order 2. Ceta'cea. Adapted to marine life. Examples: whale, porpoise. 

Orders. Sire'nia. Fishlike in form; pectoral limbs paddle-like. Examples: manatee, dugong. 

Order 4. Roden'tia. Incisor teeth chisel-shaped, usually two above and two below. Ex- 
amples: beaver, rat, porcupine, rabbit, squirrel. 

Order 5. Ungula'ta. Hoofs ; teeth adapted for grinding. Examples : (a) odd-toed : horse, 
rhinoceros, tapir ; (6) even-toed : ox, pig, sheep, deer. 

Order 6. Insectiv'ora. Small, insect-eating, furry or spiny covered ; long snout. Example : 

Order 7. Carniv'ora. Long canine teeth, sharp and long claws. Examples: dog, cat, lion, 
bear, seal, and sea lion. 

Order 8. Cheirop'tera. Fore limbs adapted to flight, teeth pointed. Example : bat. 

Order 9. Prima'tes. Erect or nearly so, fore appendage provided with hand. Examples : 
monkey, ape. Anatomically, man is placed with this highest group of mammals. 

Increasing Complexity of Structure and of Habits in Plants and 
Animals. — In our study of biology so far we have tried to get 
some notion of the various factors which act upon living things. 
We have seen how plants and animals interact upon each other. 

1 All except the monotremes. 


We have learned something about the various physiological pro- 
cesses of plants and of animals, and have found them to be in many 
respects identical. We have found grades of complexity in plants 
from the one-celled plant to the complicated flowering plants of 
considerable size and with many organs. So in animal life, from 
the protozoa upward, there is constant change, the change being 
usually toward greater complexity of structure and functions. A 
worm is a higher type of life than a protozoan, because its struc- 
ture is more complex. A fish is a higher type of animal than a 
worm, for this same reason, and also because it has an internal 
skeleton. It is a vertebrate animal. 

We have now learned that animals may be arranged in groups, 
beginning with very simple one-celled forms and culminating with 
man himself. These groups are believed by scientists to represent 
different stages in the complexity of development of life on the 
earth. Geologists find in the rocks of this earth many fossils, or 
remains of plants and animals that have long been dead. They 
teach that the earliest forms of life upon the earth were very 
simple, and that gradually more and more complex forms ap- 
peared, as the rocks formed latest in time show the most highly 
developed forms of plant and animal life. 

Man's Place in Classification. — Man is the only creature that 
has moral and religious instincts. Although we know that man is 
separated mentally by a wide gap from all other animals, in our study 
of biology we must ask where man is to be placed. If we attempt 
to classify man structurally, we see at once that he must be 
placed with the vertebrates because he has a vertebral column. 
Evidently, too, he is a mammal, because the young are nour- 
ished by milk secreted by the mother, and because his body 
has at least a partial covering of hair. Finally, man is placed 
in the highest order of mammals, the primates, because he walks 
erect and his fore appendages (the arms) are each provided with 
a hand. 

Development of Man. — Undoubtedly there once lived upon the 
earth races of men who were much lower in their civilization than 
the present inhabitants. They were probably nomads, wandering 
from place to place, feeding upon wild fruits, seeds, roots, and what- 
ever living things they could kill with their hands. Gradually 

MAN 251 

they must have learned to use weapons and thus to kill prey more 
easily, first using rough stone implements for this purpose. As 
men became more civilized, they used implements of bronze and 
of iron. About this time the subjugation and domestication of 
animals began to take place. Men also began to cultivate the 
fields and to have fixed places of abode. The beginnings of civili- 
zation were long ago, but even to-day mankind is not entirely 

The Races of Man. — At the present time there exist upon the 
earth fiv§ races or varieties of man, each very different from the 
others in instincts, social customs, and, to an extent, in structure. 
These are the Ethiopian or negro type, originating in Africa ; the 
Malay or brown race, from the islands of the Pacific ; the Ameri- 
can Indian ; the Mongolian or yellow race, including the natives of 
China, Japan, and the Eskimos ; and finally the Caucasians, 
including the white inhabitants of Europe and America and the 
Hindus and Arabs of Asia. 

Summary. — Plants and animals may be classified into species, 
genera, families, orders, classes, and phyla. All classification is 
based on homologies or likenesses in structure and position of 
organs. Increasing complexity of structure is used as a basis for 
the arrangement of plants and animals in series. A comparison 
of such a series as is given in the preceding pages with fossils shows 
us that the older the rocks, the more simple are the animal and 
plant forms found in them. The fossils of complex forms are 
found only in the later rocks. As respects civilization, the races 
of mankind were once not so highly developed as they are now. 
But even now many races are very backward and not entirely 

Pboblem Questions 

1. Why are plants and animals classified? 

2. What is the basis for classification ? 

3. About how many species of plants are there ? About how many species 
of animals ? 

4. Why are the insects such a large group ? 

5. Why is homology a basis for classification ? 

6. Could something be analogous without being homologous, or homologous 
without being analogous? Give examples. 

7. What reasons have we for placing man as the highest animal? 


Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Beebe, The Bird. Henry Holt and Company, 

Ditmars, The Reptiles of New York. Guide Leaflet 20. American Museum 

of Natural History. 
Ditmars, The Reptile Book. Doubleday, Page and Company. 
Hornada}'-, American Natural History. Charles Scribner's Sons. 
Jordan and Evermann, American Food and Game Fishes. Doubleday, Page 

and Company, 
Parker and Haswell, Textbook of Zoology. The Macmillan Company. 
Riverside Natural History. Houghton Mifflin Company. 
Transeau, General Botany. World Book Company. 




Problems: What are bacteria and how may we obtain and grow 

What are conditions favorable and unfavorable to the growth of 

What are some means used to destroy bacteria? 

What are some diseases caused by bacteria? 

Laboratory Suggestions 

Problem. Where are bacteria found? 

Demonstration. How bacteria are grown. 

Demonstration. How to make culture media. 

Demonstration. How to obtain a pure culture of bacteria. 

Home experiment. Conditions favorable for the growth of bacteria. 

Demonstration. Effect of light on bacterial growth. 

Demonstration. Effect of heat on bacterial growth. 

Experiment. Use of disinfectants. 

What is Health ? — The body has been likened to an engine or 
machine and we have found that in some respects this simile holds 
true. The body and the engine are each made of many parts and 
run more or less automatically. Both require fuel and oxygen to 
do work, both produce wastes, and both must have frequent rest 
if they are to do efficient work. Both the machine and the body 
eventually may wear out ; and, if we carry the simile to the end, 
both machine and body are destroyed. But we do not speak of a 
sick machine, though we do speak of a sick person. What, then, 
is health ? It is evidently a state in which the human machine runs 
efficiently. It is a state of well-being, or being well. 




What causes Disease ? — There are many causes of disease, 
although there is usually only one primary cause in each instance. 
A person may so abuse his body machine through lack of sleep or 
exercise or proper food that soon his body will not function prop- 
erly. He may become nervously out of sorts and imagine himself 
ill, and succeed pretty well in making the delusion a reality. He 
may poison his body with alcohol or nicotine and injure some of his 
internal organs so that he never recovers his former efficiency. 
He may meet with an accident and be crippled or otherwise in- 
jured. Or he may be attacked by some of man's microscopic 

foes, bacteria or protozoa, and suffer 
from an infectious disease. The last- 
named cause is by far the most usual 
and may be said to induce much more 
than half of the common ills that cause 
pain and sorrow. 

How we get Bacteria for Study. — 
If any one should express doubt that 
bacteria cause disease, it is easy to 
prove that they do. But we must be- 
gin by proving that there are such 
things as bacteria. Since these tiny 
plants, '' man's invisible friends and 
foes," are to be found " anywhere but 
not everywhere " in nature, it is easy 
to obtain them with the proper means. 
To obtain cultures of bacteria for study, it is first necessary to 
find some material in which they will grow, then to kill all living 
matter in this food material by heating it to the boiling point (212° 
Fahrenheit) for half an hour or more (this is one method of steriliza- 
tion), and finally to protect the culture medium, as this food is 
called, from other living things that might feed upon it. 

Many bacteria thrive in a mixture of beef extract and gelatin 
or agar-agar, a substance derived from seaweed. This mixture, 
after sterilization, is poured into flat dishes with loose-fitting 
covers which have been previously sterilized also. These Petri 
dishes, so called after their inventor, are the traps in which we 
collect and study bacteria. 

Steam sterilizer. 


Where Bacteria may he found. Growths of bacteria may be 
obtained on dishes prepared in the following ways : 

(a) exposing to the air of the schoolroom ; 

(6) exposing in the halls of the school while pupils are passing ; 

(c) exposing in the halls of the school when pupils are not mov- 

(d) exposing at the level of a dirty and much-used street ; 

(e) exposing at the level of a well swept and little used street ; 
(/) exposing in a park or elsewhere among trees ; 

(g) exposing in a factory building ; 

(h) touching the medium with the fingers ; 

(i) touching the medium with fingers moistened with saliva ; 

(j) touching the medium with decayed vegetable or meat ; 

(k) touching the medium with dirty coin or bill ; 

(I) placing in dish two or three hairs from one's head ; 

(m) keep one dish, the " check " or " control," unexposed. 

This list might be prolonged indefinitely. 

Place all of the dishes in a moderately warm place (a closet in 
the schoolroom will do) for the 
process called incubation. After a 
day or two, little spots, brown, yel- 
low, white, or red, will begin to 
appear. These spots, which grow 
larger day by day, are colonies made 
up of millions of bacteria ; and 
probably each colony arose from a 
single bacterium. 

How we may isolate Bacteria of 
One Kind from the Other. — In 

order to get bacteria of a given Colonies of bacteria growing in a 
T . T , , 1 .. 1 Petri dish. 

kmd to study, it becomes necessary 

to grow them in what is known as a pure culture. This is done 
after first growing the bacteria in some medium such as beef broth 
or gelatin, or on potato.^ When the colonies of bacteria appear 

^ For directions for making a culture medium, see Hunter, Laboratory Problems 
in^ivic Biology. Culture tubes may be obtained, already prepared, from Parke, 
Davis, and Company or other good chemists. 



A pure cultuifc ut b^ctencx. ^NuLice 
that the bacteria are all the same size 
and shape. 

or the beef broth becomes cloudy, one form may be isolated from 
the others by the following process: a platinum needle is first 

passed through a flame to sterilize 
it. After the needle is cooled it is 
dipped in a colony containing the 
kind of bacteria we wish to study. 
The needle is then quickly drawn 
across the surface of a dish of 
sterile culture medium, and the 
dish is immediately covered to pre- 
vent any other forms of bacteria 
from entering. When we have suc- 
ceeded in isolating a certain kind 
of bacteria in a given dish, we have a pure culture. 

Size and Form. — In size, bacteria are the most minute plants 
known. A bacterium of average size is about -g-^ of an inch in 
length, and perhaps 2^^-00" c>f an inch in diameter. Some species 
are much larger, others smaller. They are so small that several 
million are often found in a large drop of impure water or sour milk. 
Three well-defined forms of bacteria are recognized : a 
spherical form called a coccus; a rod-shaped bacterium, 
the bacillus; and a spiral form, the spirillum. Some 
bacteria are capable of movement when living in a fluid. 
Tiny lashlike threads of protoplasm called flagella 
project from the body, and by a rapid movement cause 
locomotion. Bacteria reproduce with almost incredible 
rapidity. It is estimated that a single bacterium, by a 
process of division called fission, might if unchecked 
give rise to nearly 17,000,000 others in twelve hours. 
Under unfavorable conditions bacteria stop dividing 
and form rounded bodies called spores. The spore is 
usually protected by a wall and can withstand very un- 
favorable conditions of dryness or heat ; even boiling 
for several minutes will not kill some forms. 

Where Bacteria are most Numerous. — As the result of our 
studies, we may draw some inferences concerning the presence of 
bacteria in our own environment. They are evidently present 
in the air, and in greater quantity in air that is moving than in 

^ ^^ 

forms of 



quiet air. Why? That they stick to particles of dust can be 
proved by placing a little dust from the schoolroom on a culture 
medium. Bacteria are present in great numbers where crowds of 
people live and move. The air from dusty streets of a populous 
city contains more bacteria than does the cleaner air of a village 
street. The air of a city park contains relatively few bacteria 
when compared with the air of a near-by street; the air of the 
woods or high mountains, fewer still. Why? Our previous 
experiments have shov/n that 
dirt on our hands, the mouth 
and teeth, decayed meat and 
vegetables, dirty money, the 
very hairs of one's head, are 
all carriers of bacteria. 

Fluids the Favorite Home 
of Bacteria.^ — Tap water, 
standing water, milk, vinegar, 
wine, cider, all can be proved 
to contain bacteria by experi- 
ments similar to those already 
suggested. Spring or artesian 
well water would have very 
few, if any, bacteria, while 
the same quantity of river 
water, if it held any sewage, 

might contain untold millions of these little organisms. Moisture 
is absolutely necessary for bacterial growth ; consequently, keeping 
material dry will prevent the growth of germs. Bacteria grow 
most freely in fluids. 

Food of Bacteria. — Bacteria are living and contain no chloro- 
phyll, and we should expect them to need protein food in order 
to grow. Such is not always the case, for some bacteria seem 
to be able to build up protein out of simple inorganic nitro- 
genous substances. If, however, we take several food sub- 
stances, some containing much protein and others not so much, 
we find that the bacteria cause decay in the proteins almost at 
once, while other food substances are not always attacked by 

Growth of bacteria in a drop of impure 
water allowed to run down a sterilized cul- 
ture in a dish. 


What Bacteria do to Foods. — ^Tien bacteria feed, they dis- 
solve the food substances by means of enzjTxies which they secrete. 
The food is decomposed and eventual!}^ rots. The material left 
behind after the bacteria have finished their meal is quite different 
from its original form. It is broken down by the action of the 
bacterial enzjmies into gases, fluids, and some solids. It has a 
characteristic '^ rotten " odor, and contains poisons which come 
as a result of the work of the bacteria. 

Bacteria affected by Light. — If we cover with black paper one 
half of a Petri dish in which bacteria are growing, and then place 
the dish in a light warm place for a few days, the growth of bac- 
teria in the exposed part of the dish will be found to be checked, 
while growth continues in the covered part. It is a matter of com- 
mon knowledge that disease germs thrive where dirt and darkness 
exist and are killed by long exposure to sunlight. This shows us 
the need of light in our homes, especially in our bedrooms. 

Bacteria and Air. — We have seen that plants need oxygen 
in order to perform the work that they do. This is equally 
true of all animals. But not all bacteria need air to live ; in fact, 
some are killed bj^ the presence of air. Bacteria which live with- 
out free oxj^gen are called anaerob'ic bacteria. They need oxj^gen, 
as do aU other hving things, but they obtain it by breaking down 
the foods on which they live, and utilizing the oxygen freed in this 

Sterilization. — Bacteria grow very slowly, if at all, in the tem- 
perature of an ice box, very rapidly from 70° to 98°, and much less 
rapidly (or are killed) at a higher temperature. Those bacteria 
which form spores resist a great deal of heat and may even be 
boiled for some time without injury. The practical lessons drawn 
from these facts are many. We boil our drinking water if we are 
uncertain of its purity ; we cook foods that we believe might har- 
bor bacteria, and thus keep them from spoiling. The industry 
of canning is built upon this method of sterilization. 

Pasteurization. — Milk is one of the most important food sup- 
plies of mankind. It is also one of the most difficult things to 
get in good condition. This is due in part to the fact that milk is 
often produced at long distances from the place where it is used 
and must be brought first from farms to the railroads, then shipped 



by train, taken to the milk supply depot, bottled, and again taken 
by delivery wagons to the consumers. During each successive 
handling and exposure to the air the milk receives more bacteria. 
When we remember that much of the milk used in San Francisco, 
St. Louis, Chicago, New York, and other large cities is from twelve 
to thirty-six hours old before it reaches the consumer, and when 
we realize that bacteria grow very rapidly in milk, we see the need 
of finding some way to 
protect the supply so as 
to make it safe, par- 
ticularly for babies and 
young children. This is 
done by pasteurization, a 
method named after the 
French bacteriologist, 
Louis Pasteur. To pas- 
teurize milk the best 
method is to heat it to a 
temperature of not over 
140° Fahrenheit for 
twenty minutes. By 
such a process all harm- 
ful germs and most of the others are killed and the milk does 
not sour so soon. Some large milk companies pasteurize their 
city supply by a rapid method at a much higher temperature, 
but this slightly changes the flavor and destroys the enzymes and 
vitamins in the milk. 

Disinfection.^ — Frequently it becomes necessary to destroy 
bacteria with chemicals. This process is called disinfection. 
While sunlight, dry heat, steam, and electricity kill germs, we 
commonly apply the term disinfectant to such substances as iodine, 
potassium permanganate, chloride of lime, carbolic acid, formalin 
or formaldehyde, lysol, and bichloride of mercury. Of these, the 

^ Experiment to determine the most effective disinfectants. Use tubes of 
bouillon containing different strength solutions of formaldehyde, lysol, iodine, 
carbolic acid, and bichloride of m.ercury or other disinfectants. Expose all 
the tubes to the air for half an hour, then plug with cotton wool. Examine 
after one week. Results. Conclusions. 

Pasteurization of milk. 


last named is one of the most powerful as well as the most dan- 
gerous to use. As it attacks metal, it should not be used in a metal 
pail or dish. It is commonly put up in tablets which are mixed 
to form a 1 to 1000 solution. Care must be taken of both the 
tablets and the solution to avoid a possible accidental poisoning. 
Formaldeh^^de in solution, called formalin, is used as a disin- 
fectant. When vaporized, it sets free an intensely pungent gas 
which is sometimes used for disinfecting the sick room after the 
patient has been removed. 

Carbolic acid is an excellent disinfectant although it will not 
kill spores of bacteria. If used in a solution of about 1 part to 25 

of water, it will not burn the skin. It 
is of particular value in disinfecting skin 
wounds. Lysol is another excellent 
disinfectant, because it can be used 
with soap. Iodine is often used as a 
skin disinfectant and in open wounds. 
Chloride of lime is an old-time but good 
disinfectant ; it also is a deodorant. 
One of the newest disinfectants is mer- 

A single cell scraped from the ^ . ^x. mi ±. 

roof of the mouth and highly Bacteria cause Disease. — The most 
magnified. The little dots are harmful bacteria are those which cause 

bacteria, most of which are ,. ,• i i i • i i-t j • 

harmless. diseases 01 plants and animals. Certain 

diseases of plants — blights, rots, and 
wilts — are of bacterial nature. These do much damage annually 
to fruits and other parts of growing plants useful to man as food. 
But by far the most harmful are the bacteria which cause many 
diseases in man. They accomplish this by becoming parasites in 
the human body. Millions upon millions of bacteria exist in the 
human body at all times — in the mouth, on the teeth, and espe- 
cially in the lower part of the food tube. Some in the food tube 
are believed to be useful, some harmless, and some harmful ; others 
in the mouth cause decay of the teeth, while a few species may cause 
disease. Such disease-causing bacteria are called pathogen'ic. 

It is known that bacteria, like other living things, take in food, 
form organic wastes within their own bodies, and give off some 
of them. These wastes, called toxins, are poisonous to the host 


on which the bacteria Hve, and cause the symptoms of certain 
diseases. Each species of bacteria forms its own specific toxin, 
and this has a specific action on the body, causing the symptoms 
of a specific disease. As bacteria can multiply rapidly in the body, 
they may become very numerous before the body defenses (see 
page 168) gain control of the situation. When the bacteria die, 
as they may in great numbers during the progress of the disease, 
their bodies break down, and the released protoplasmic constitu- 
ents, particularly the proteins, separate from each other and split 
into smaller and smaller molecular groups, as do the proteins when 
changed to amino-acids during digestion. These split proteins, as 
they are called, are extremely poisonous to the body tissues and 
act as toxins in the body, causing many of the characteristic 
symptoms of disease. 

Some bacteria break down the body tissues, besides producing 
toxins. They may destroy the intestinal lining, or destroy the 
blood corpuscles, or break down tissues in wounds, thus causing 
specific symptoms of disease. 

It is estimated that germ diseases cause annually over 50 per 
cent of the deaths of the human race. A very large proportion 
of these diseases might be prevented if people were educated 
sufficiently to take the proper precautions to prevent the spreading 
of bacteria. These precautions might save the lives of some 
3,000,000 people yearly in Europe and America. Tuberculosis, 
typhoid fever, bubonic plague, diphtheria, pneumonia, blood 
poisoning, and a score of other germ diseases ought not to exist. 
A good deal of the present misery of this world might be prevented 
and this earth made cleaner and better by the cooperation of young 
people now growing up to be our future home makers. 

How we get Germ Diseases. — Germ or infectious diseases 
enter the body either by way of the mouth, nose, or other body 
openings, or through a break in the skin. They may be carried 
by means of air, food, or water^ but are more often transmitted 
directly from the person who has the disease to a well person. 
They may be acquired through personal contact ; from the mouth 
spray of persons who have certain diseases ; by handling or using 
articles, such as towels, handkerchiefs, cups, or dishes used by 
sick persons ; or by drinking or eating foods which have received 

H. NEW CIV. BIOL. — 18 





some of the germs. From this it follows that if we know how 
a given disease is communicated, we ma}^ protect ourselves from 
it and aid the civic authorities in preventing its spread. 

Tuberculosis. — One of the diseases responsible for the greatest 
number of deaths, perhaps one tenth of the total on the globe, is 
tuberculosis. It is estimated that of all people ahve in the United 
States to-day, 5,000,000 will die of this disease. Fisher estimates 
that tuberculosis costs this country between $500,000,000 and 

81,000,000,000 a yesLY, by 
its toU of death, loss of 
work, maintenance of hos- 
pitals, sanatoriums, etc. 
But this disease is slowly 
but surely being overcome. 
It is believed that within 
perhaps fifty years, with 
the aid of good laws and 
sanitary living, it might 
become almost extinct. In 
Xew York state the death 
rate has decreased from 
186.8 per 100,000 in 1900 
to 87.8 in 1923, and equalh^ good records come from other parts of 
the United States. 

Tuberculosis is caused by the growth of bacteria,, called the 
tubercle hacilU, within the lungs or other tissues of the human body. 
In the lungs they form httle tubercles full of germs, which close up 
the dehcate air passages, while in other tissues they may cause 
hip-joint disease, scrofula, lupus, and other diseases, depending 
on the part of the bodj^ they attack. Tuberculosis may be con- 
tracted by taking in bacteria through the mouth from people who 
have the disease, or possibly by drinking milk from tubercular 
cows, for the germ that affects cattle causes some of the tuber- 
culosis in children. Dr. William H. Park, a noted authority on 
bovine (cow) tuberculosis, states that in a large number of cases 
investigated by him 57 per cent of abdominal tuberculosis in 
very A^oung children and 47 per cent of such tuberculosis in 
children under five years of age was of the bovine type. For- 

1850 1860 1870 1880 1890 1900 1910 1920 1930 

Curve sho"wing a decreasing death rate from 
tuberculosis ; the number of deaths each year 
per 100.000. 


tunately, the germs of bovine tuberculosis can be kiUed by pas- 
teurization of milk of doubtful purity. Tuberculosis is often com- 
municated from a consumptive to a well person by kissing and by 
using the same cup, plate, towels, or other unsterilized things used 
by consumptives. 

Although there are always some tuberculoses germs in the dusty 
air of an ordinary city street, and although we may take some of 
these germs into our bodies at any time, yet the bacteria seem able 
to gain a foothold only under certain conditions. In most persons 
the body resists the invasion of these germs and they are killed 
before they can do harm. It is only when the tissues are in a worn- 
out condition, when we are ^' run down," as we say, that the par- 
asite may obtain a foothold in the lungs or other organs. Even 
if the disease gets a foothold, it is quite possible to cure it if it is 
taken in time. The disease may be arrested, and a permanent 
cure is often brought about, by a life in the open air, the patient 
living and sleeping out of doors, taking plenty of nourishing food, 
and very little exercise. The object of this kind of life is to build 
up the body resistance, so that the germs are rendered incapable of 
doing harm. 

Tuberculosis is a serious disease to combat, because of the con- 
ditions which help to cause it. Contrary to common belief, it is 
not inherited ; but unfortunately in families where there are tuber- 
culous persons, it is difficult to prevent giving the germs to people 
living with them, especially if they live in small crowded homes 
with little ventilation. Children of tuberculous parents are often 
handicapped by a weak constitution and are therefore more sus- 
ceptible. Tuberculosis in the homes of the poor, therefore, is 
more serious than in the homes of the well-to-do, because of 
crowded surroundings and lack of proper conditions of rest, food, 
and peace of mind for the patient. 

Diphtheria. — Of the many other diseases traced to bacteria, 
diphtheria is one of the best known. It is caused by a germ which 
grows rapidly in the throat and forms a false membrane there. 
But the most serious results come from the toxin, which gets into 
the blood and not only causes discomfort and fever but also may 
have very serious after-effects on various body organs. As diph- 
theria is a throat disease, it may easily be conveyed from one per- 




son to another by kissing, by putting into the mouth objects which 
have come in contact with the mouth of the patient, or by food 
which contains the germs, and particularly through the droplets 
or spray which comes from the mouth of the person having the 

Other Diseases spread through Mouth Spray. — Influenza, 
pneumonia, whooping cough, and certain kinds of colds, and many 

of the so-called children's dis- 
eases, are caused by bacteria 
or other microscopic organ- 
isms. Nearly all are spread 
by direct contact with persons 
having the disease, and the con- 
tact in most cases is brought 
about by the ^'droplet method" 
of infection . In our army dur- 
ing the World War, influenza, 
coupled with pneumonia, was 
responsible for fourteen times 
as many deaths as were caused 


/ / 


\ \ 



\ \ 

hydc Pdrk Dorchester 


This figure shows how a milk route might 
spread diphtheria. X is a farm on which 
occurred a case of diphtheria that was re- 
sponsible for all the cases along milk routes 
A and F in Hyde Park, Dorchester, and 
Milton. How would you explain this ? 

by shells and poison gases. This disease is periodically epidemic, 
the last bad outbreak previous to this being in 1889. Influenza is 
apparently spread largely by human carriers, or people who have 
a slight attack but are capable of passing the disease on in its most 
serious form. 

Typhoid Fever. — Typhoid fever, not many years ago, was one 
of the most common germ diseases in this country and Europe. 
But knowledge of the cause and prevention has greatly decreased 
its death rate in recent years. Typhoid germs live in the intestine 
and from there get into the blood and are carried to all parts of the 
body. The products which they make cause the fever so charac- 
teristic of the disease. The germs multiply very rapidly in the 
intestine and are passed off from the body with the excreta from 
the food tube. If these germs get into the water supply of a town, 
an epidemic of t3q)hoid will result. In one such epidemic there 
were 5000 cases of typhoid in a city of only 30,000 inhabitants. 
Chicago and other cities which obtained their drinking water 
from lakes polluted with sewage always had a high death rate from 



typhoid. In the year 1892, 1489 persons died in Chicago from 
typhoid. To-day, when the city is three times as large, the total 
number of deaths from typhoid is less than 400 in a year. How 
can you account for this difference ? 

How sewage containing typhoid bacteria may get into drinking water : c, cesspool. 

Another source of infection is milk. Frequently epidemics 
have occurred which were confined to users of milk from a certain 
dairy. Upon investigation it was found that a case of typhoid 
had occurred on the farm where the milk came from, that the germs 
had washed into the well, and that this water was used to wash the 
milk cans. Once in the milk, the bacteria multiplied rapidly, so 
that the milkman gave out cultures of typhoid in his milk bottles. 

A third and more serious method of spread of typhoid comes 
through the agency of carriers. These are people who have had 
typhoid and who still harbor the living germs in their bodies. The 
least carelessness on their part may result in the spread of typhoid 
to unsuspecting people. Several epidemics of typhoid have been 
traced to carriers who worked in dairies or on farms which produced 
milk. The well-known ^' Typhoid Mary " through her careless 
habits gave typhoid to people wherever she was cook. Still an- 
other method of spreading typhoid is through carelessness in 
preparation of uncooked vegetables. Several epidemics of typhoid 
have been traced to raw oysters which were '' fattened " for the 
market in water that was contaminated with sewage. 

Watchfulness of our water, milk, and food supplies is necessary 
if we are to prevent epidemics or sporadic outbreaks of typhoid. 


Septic Sore Throat. — This disease is characterized by very 
severe sore throat and fever, and is often followed by heart or 
kidney trouble. This is another milk-borne disease, which is 
caused by a streptococ'cus. The disease is probably given to cows 
by humans who may be carriers. Thus the cow may harbor the 
germ for several weeks and persons drinking unpasteurized milk 
from such a cow may take the disease. Several severe epidemics 
have been recorded, in Baltimore, Chicago, and other cities, but 
the worst was an outbreak of 2000 cases in Boston, in 1911. 

Tetanus. — The bacterium causing tet'anus is another toxin- 
forming germ. It lives in dust and dirt and is often found on the 
skin. It enters the body through cuts or bruises. It seems to 
thrive best in less oxygen than is found in the air. It is therefore 
important not to use court-plaster over wounds which such germs 
may have entered. The low death rate from tetanus in the World 
War was due largely to the fact that wounds were washed with 
powerful antiseptics and anti-tetanus serum was administered as 
soon as possible after the wounded were reached. 

Other Diseases Caused by Bacteria. — A group of bacteria 
which cause pneumonia, erysipelas, and other common infections 
besides septic sore throat are the so-called streptococci. Other 
coccus forms, the staphylococci (staf-i-l6-k6k'sl) , are responsible for 
boils and abscesses. A micrococcus causes one of the pernicious 
venereal diseases, which produce terrible results. Other forms of 
micrococci probably cause cerebro-spinal meningitis (men-in-ji'tis), 
formerly a fatal disease of the spinal cord but now often treated 
successfully with serums. Anthrax, or splenic fever, Malta fever, 
whooping cough, bubonic plague, gas gangrene, one form of 
dysentery, cholera, and many other diseases are definitely associ- 
ated with specific forms of bacteria. Scarlet fever has recently 
been added to the list of diseases caused by cocci. Other dis- 
eases, as malaria, yellow fever, African sleeping sickness, and 
probably smallpox and measles, are due to the attack of one- 
celled animal parasites (which will be described in Chapter XXIV) . 

Summary. — This chapter has shown us that bacteria are found 
almost everywhere and can easily be studied in the laboratory. 
Fortunately, comparatively few of the many forms cause disease. 
Pathogenic or disease-causing bacteria, however, cause a large 


number of diseases which ought to be stamped out of existence 
and will be when our knowledge of them is greater. The symp- 
toms of disease are caused mainly by the products of bacterial 
activity, each species of bacteria forming its own specific toxins. 
Tuberculosis, diphtheria, pneumonia, influenza, and most children's 
diseases are transferred through mouth sprays, though there are 
other methods of transfer. Typhoid fever, once very prevalent, is 
transferred by milk, water, uncooked vegetables, and by human 
carriers. There are many other bacterial diseases, such as tetanus, 
septic sore throat, and other types of streptococcus infection. 

Problem Questions 

1. What is disease? 

2. Why are bacteria said to exist " anywhere, but not everywhere "? 

3. Why is sterilization necessary in preparing culture media for the growth 
of bacteria? 

4. Name various forms of bacteria. Can bacteria move? 

5. What conditions are most favorable for bacterial growth ? Which are 
most unfavorable? 

6. What is pasteurization ? What method is best and why? 

7. What are the most valuable disinfectants and why? 

8. What are the different methods of " taking " a germ disease? 

9. Why is tuberculosis said to be ^' a poor man's disease "? 

10. What are the best methods of fighting tuberculosis ? Is state aid wise ? 
If so, why? 

11. Is it possible to prevent taking typhoid? 

12. What would you say was the most dangerous germ disease and why ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 

Broadhurst, How We Resist Disease. J. B. Lippincott Company. 

Burnet, Microbes and Toxins in Nature. G. P. Putnam's Sons. 

Conn, Bacteria, Yeasts and Molds in the Home. Ginn and Company. 

Conn, Story of Germ Life. D. Appleton and Company. 

Coulter, Barnes, and Cowles, A Textbook of Botany, Vol. I. American Book 

Frankland, Bacteria in Daily Life. Longmans, Green and Company. 
Hough and Sedgwick, The Human Mechanism. Ginn and Company. 
Hutchinson, Preventable Diseases. Houghton Mifflin Company. 
Lee, Scientific Features of Modern Medicine. Columbia University Press 
Rosenau, Preventive Medicine and Hygiene. D. Appleton and Company. 


Problems: What is the incubation period of a disease and what 
is its significance? 

Why is quarantine necessary? 

What is natural immunity f 

What is active immunity ? What is passive immunity f 

What are antitoxins and how are they used? 

What are vaccines and what do they do ? 

Laboratory Suggestions 

Laboratory study of vital statistics. Construction of graphs of certain infec- 
tious diseases. 

Field work. Visit to a local board of health or to a hospital to learn how- 
certain tests are made and how protection against disease is obtained. 

Reasons for Quarantine. — We all know that when a person 
has a communicable disease, the doctor, acting under orders of the 
local board of health, puts the patient and sometimes the entire 
family under quarantine. Since this often seems needless, espe- 
cially if one has a mild attack of the disease, we ought to know the 
reason underlying such action. Communicable diseases become 
epidemic if they are not controlled. Measles, for example, is a dis- 
ease easily passed from one person to another. It is especially 
communicable among children, one of whom may have a very 
light case but may pass the germs to some one else who will have 
a severe attack of it. Scarlet fever, colds, and influenza are other 
diseases which are readily spread and may become epidemic. 

Since this is true, the reason for the isolation of the patient 
becomes evident. And every one should be unselfish enough to 
see this and to cooperate with the health authorities for the common 
good of the community. 




The following table shows important facts about some com- 
mon diseases. 

Means op 

Incubation Period (Approximate) 



AND Early Symptoms 


Chicken pox . . 

Discharges from nose 
or throat of a pa- 

21 days. Rash. 

Diphtheria . . 

Nose or throat dis- 
charges; sometimes 
infected milk 

2 to 5 days. Begins like a cold. 

Measles . . . 

Nose or throat dis- 

9 to 11 days. Begins like a cold. 


Reddish spots appear on the 
third day. 

German measles . 

Nose or throat dis- 

Unknown, though longer than 



Mumps .... 

Nose or throat dis- 

Unknown, probably about 2 


weeks . Pain in sal ivary glands . 

Infantile paralysis 

Nose, throat, or bowel 

Not known. Fever, headache. 

discharges of pa- 

vomiting, weakness of one or 

tient or carrier 

more muscle groups. 

Scarlet fever . . 

Discharges from nose. 

2 to 7 days. Begins like a cold; 

mouth, ears. In- 

in 24 hours evenly diffused 

fected milk 

bright red spots under skin. 

Smallpox . . . 

All discharges of a pa- 

About 12 days. Fever and back- 

tient; particles of 

ache. Red shothke pimples on 

skin or scabs 

face and hands, become blisters. 

Septic sore throat . 

Discharges from nose 
or mouth 

Varies with resistance. 

Whooping cough . 

Discharges from nose 

14 days. Cough ; worse at night. 

or mouth 

"Whooping" develops in about 
two weeks. 

Incubation Period of Disease. — Quarantine regulations often 
affect not only the person having the disease, but also all those of 
the family who were " exposed " ; that is, who came in personal 
contact with the person who has the disease. If, for example, you 
have measles, the doctor will keep at home the other children in the 
family who have not had the disease. The period of quarantine 
for measles lasts in most states fifteen days. Why this precaution ? 

Consider what we already know of germs. We found it took a 
certain length of time for colonies of germs to appear in a culture 
medium after exposure. In the same way it takes a certain 
amount of time in the case of a disease for the germs to become 


so abundant in the body that the}^ give off sufficient toxins to 
cause the symptoms of the disease. This period, between the time 
when the germs enter the body and the time the symptoms of 
disease appear, is called the incubation period. Since this period 

left school 
Oct 15th, ill. 
No physicidP 



^sdt with Jams' 

[Developed measles' 




^pldyedmfh John 


measles MM. 



The failure to recognize James's illness as measles resulted in its spread to three 
other cases. Strict quarantine prevented its further spread. 

varies for different diseases, the period of quarantine also varies, 
as seven days for scarlet fever, fourteen days for whooping cough, 
twenty-one days for chicken pox. 

The Meaning of Immunity. — It is a matter of common knowl- 
edge that some persons in a family will have a very light attack of 
a communicable disease, while others may have it severely. Some 
one else may be exposed again and again to this same disease and 
not take it, because he is immune to that particular disease, while 
those who take it are susceptible to its attack. Immunity against 
disease may be individual, or it may be racial. The Negro race, 
for example, is very susceptible to measles and tuberculosis and in 
a lesser degree to yellow fever. White people are much more sus- 
ceptible to malaria, yellow fever, and smallpox. There are also 
great differences as to immunity from the same germ in different 
species of animals. Tuberculosis of the bovine type may occur in 
children as well as in cattle, hogs, and horses. The human tuber- 


culosis germ attacks only guinea pigs, monkeys, and man. Small- 
pox and cowpox are probably caused by the same organism. 
Plague attacks rats, ground squirrels, mice, and guinea pigs, as 
well as man. A long series of laboratory tests show that most germs 
that cause illness in man develop ordinarily in man only, while a 
few diseases, Hke anthrax and glanders, are primarily diseases of 
certain animals but may attack man. 

Immunity may be modified by External Conditions. — A certain 
amount of immunity is evidently natural to individuals, races, or 
species, but there is much variation, as we have seen, even among 
individuals of the same family. Resistance to disease also is 
modified by the condition of the individual exposed. Overworked, 
tired, and ''run-down" persons are much more likely to take germ 
diseases than those who are in good physical trim. Resistance to 
disease may also be weakened by the use of drugs and alcohol 
as shown by the susceptibility of heavy drinkers to pneumonia. 

Acquired Immunity. — It has been a matter of common knowl- 
edge for centuries that persons who have infectious diseases do not 
usually have them a second time. A Greek historian, describing a 
visitation of plague in Athens, more than twenty centuries ago, noted 
that those who had plague and recovered were safe from it there- 
after. The Chinese, in order to make their children immune to 
smallpox, gave them the disease in a mild form by placing in the 
nose a little of the pus from one of the eruptions. And it was the 
chance statement of a dairymaid in England when she said, '' I've 
had cowpox and can't take smallpox " that led Edward Jenner 
(page 407) to make his first experiments that have resulted in 
almost stamping out smallpox through vaccination. And so to-day 
when we think of acquired immunity obtained by this or that 
antitoxin or antiserum or vaccine, we must remember those 
pioneers, Jenner and Pasteur (page 408), who took the first steps 
in controlling germs, and began the work which may result finally 
in preventing most germ diseases. 

How Immunity is gained. — We have already seen that the 
blood contains small amounts of various specific substances, known 
collectively as antibodies (page 165). These help the cells of the 
body combat harmful bacteria, the poisons or toxins which they 
give out, and the poisonous "split proteins" which are thrown 


into the blood when these bacteria die. When any protein sub- 
stance decays, it breaks down into simpler substances, as in diges- 
tion in our body. Some of these simpler proteins are poisonous 
and are called ptomaines (t5'ma-inz ; Gr. ptoma, dead body). 
Ptomaine poisoning, while not so common as was once thought, 
often causes discomfort and even death. Two other kinds of 
protein poisoning have recently been discovered, one caused by 
certain foods which produce eczema and other skin diseases, and 
another caused by the pollens of weeds, trees, or grasses and other 
foreign proteins, such as particles of feathers of geese and chickens, 
or hair from dogs, cats, horses, and other animals. Snake venoms 
are yet another example of poisonous proteins. 

All toxins, when they enter the human body, cause the body 
cells to react to the poison. If the cells are able to manufacture 
antibodies rapidly enough to counteract the work of the bacteria or 
their poisons, we recover from the disease. In such a case as this, 
the body cells do the work in fighting the disease and the immunity 
thus acquired is said to be active. In case the body cells themselves 
do not work, and, instead, an antitoxin is used, which is manufac- 
tured outside the body, we have an example of passive immunity. 
Let us consider the latter case first, as it is easier to understand. 

Passive Immunity. — An example of passive immunity is that ob- 
tained by the antitoxin treatment for diphtheria. This treatment, 
as the name denotes, is a method of neutralizing the toxin caused 
by the bacteria in the system. It was discovered by a German, 
Von Behring, that the serum of the blood of an animal immune to 
diphtheria is capable of neutralizing the poison produced by the 
diphtheria-causing bacteria. Horses develop large quantities of 
antitoxin when given the diphtheria toxin in gradually increasing 
doses. The serum of the blood of these horses is then carefully 
prepared and is used to inoculate the patient suffering from or 
exposed to diphtheria, and thus the disease is checked or prevented 
altogether. The laboratories of boards of health prepare this 
antitoxin and supply it fresh for public use. 

It has been found from experience in hospitals that deaths from 
diphtheria are largely preventable by the early use of antitoxin. 
It is therefore advisable, in a suspected case of diphtheria, to have 
antitoxin used at once. 



Schick Test and its Value. — By the Schick test it is possible to 
determine if a person is immune to diphtheria. A very minute dose 
of diphtheria toxin is injected under the skin of the forearm. If 

the person is immune, no reaction takes 
place, because the blood is provided 
with antitoxins. But if the person is 
susceptible, some hours later a slight 
red spot appears where the toxin was 
injected. This is a danger signal and 
shows that the person would take 
diphtheria if exposed to it. To such 
a person a treatment, known as the 
toxin-antitoxin treatment, is given. 
100 cases of diphtheria when Small amouuts of a mixture of diphthe- 

antitoxin is used on different •,• i I'l • ••xi'x 

days after the disease starts. "a toxm and antitoxm are mj ected mto 

the susceptible person, with the result 
that he becomes immune by a combination of active and passive 
immunity. This treatment has been tried with thousands of 
school children in the city of New. York, with the result that the 
death rate from diphtheria 


Ddy hi 

Early use of antitoxin saves 
lives. Number of deaths per 




•Tfie Schick test and 
treatment be^an to 
stiQw effect tiere 

dropped still lower than 
before its use (see chart). 

The Dick test and treat- 
ment promise to do as 
much in combating scarlet 
fever as the Schick test 
has done in reducing the 
death rate from diphthe- 
ria. In the Dick test a 
diluted toxin produced by 
the bacteria which cause 
scarlet fever is injected 
into the arm. A redness 
indicates that the person 

is susceptible to scarlet fever. Treatment is then given with an 
antiserum which gives the body immunity from this disease. 

Other Antitoxins. — Tetanus, commonly called lockjaw, once 
a much-dreaded infection, has now been almost stamped out 

Annual number of deaths from diphtheria per 
100,000 of population in the state of New York, 
1885 to 1925. 



through the use of a tetanus antitoxin. During the World War 
soil-infected wounds were treated with this antitoxin and as a 
result the death rate from tetanus was much lower than in previ- 
ous wars. An antitoxin was also used successfully against gas 
gangrene. Antitoxins are also used for certain types of dysentery 
and against snake venoms. 

Active Immunity. Vaccination against Smallpox. — In 1796 
Jenner first proved that inoculation with pus taken from a cow was 
capable of preventing smallpox. Years later Louis Pasteur proved 
that inoculation of chickens with an old weakened culture of chicken 
cholera bacteria caused the chickens to be slightly ill for a short 
time, but made them immune to chicken cholera. Their body ceUs 
Were stimulated by the weakened germs to manufacture antibodies 
which soon got the better of the germs and provided immunity. 

So it is with vaccination against smallpox. The virus or pus 
used for inoculation contains germs of cowpox, which is probably 
a weakened smallpox organism. Therefore when vaccination 
" takes/' the body builds up a resistance to the germs thus in- 
troduced, which ends in obtaining immunity against smallpox. 

Smallpox has been in the past a great scourge ; 90 out of every 
100 persons in Europe used to have it. As late as 1898, in Russia 
over 50,000 persons lost their lives from this disease in a year. 
In some places smallpox has been brought under absolute control 
by vaccination, though in other places, unfortunately, there are 
outbreaks, due to the fact that some people do not beheve in 
vaccination. The diagram tells its own story. 



78:7 Colored 

6S White 

132.7 Colored 

lU mite 

Deaths in 1921 and 1922 per 100,000 in a large western city. The annual num- 
ber of deaths from smallpox per 100,000 in the entire registered area of the United 
States was, in 1900, 1.9; in 1901, 3.5; in 1902. 6.6; in 1903, 4.2; since 1904 less 
than 1. 

Rabies, or Hydrophobia. — Rabies (ra'bi-ez) , which is believed 
to be caused by a protozoan parasite, is communicated in the 
sahva from one dog to another by biting. In a similar manner 



■In army 
-In civil Off 

1910 io'i^of troops vaccinated 
1911 ao'''' of troops vaccinated 
1912 m'^of troops vaccinated 


it is transferred to man. The great French bacteriologist, Louis 
Pasteur, discovered a method of treating this disease which is 
a success if begun soon after the time of the entry of the germ 
into the body. Here again the treatment is based upon the 
inoculation of the patient with a weakened organism which causes 
the body cells to set up a resistance and produce immunity. 

Vaccination against Typhoid. — In recent years typhoid fever 
has received a new check from a treatment commonly called 
'' vaccination " which 
has been introduced into 
our army and is being 
used with good effect by 
some physicians and by 
the health departments 
of several large cities. 

The figure shows the 
effect of vaccination 
against typhoid, intro- 
duced in 1910. During 
the Spanish-American 
War in the army of 
107,000 men more than 
20,000 were disabled with typhoid. Since 1914 the disease has 
been almost stamped out in the army. 

The principle underlying vaccination against typhoid is that of 
working up an active immunity by means of the introduction into 
the body of large numbers of dead typhoid germs. These organ- 
isms, with their toxins and split protein poisons, cause a disturbance 
in the body with the result that antibodies are manufactured and 
immunity secured. 

The Widal test, by means of which it is possible to determine 
at once whether a person has typhoid, has been described on page 

Active immunity is thus brought about in a number of different 
ways : by the introduction of living organisms, by the introduc- 
tion of weakened or attenuated organisms, by the introduction of 
dead organisms, and by the introduction of extracts containing 
the products of bacteria. All of these substances may be called 

01 02 03 04 05 06 

10 II 12 li I* IS 16 17 IS 19 20 II 

Annual number of deaths from typhoid fever per 
100,000 ; solid line, in the army ; dashed line, 
above shaded area, in civil population. 


vaccines. The underlying principle in all is the same; certain 
cells of the body are roused to activity, antibodies are formed, 
and the invading organisms are destroyed and their toxins neu- 
tralized. These conditions are brought about through the work 
of the lysins, precipitins, agglutinins, opsonins, and phagocytes 
already mentioned in Chapter XVI. 

Other vaccines are made and used successfully against boils, 
still another against paratyphoid, and still others for plague and 
cholera. When tests show sensitiveness to certain pollens, serums 
are made from them and a certain amount of immunity from hay 
fever is thus received. But we are just at the beginning of dis- 
coveries along this line and it will no doubt be the work of the 
physician of the future to perfect many more ways of producing 
immunity against protein poisons and germ disease. 

Summary. — This chapter has shown us that disease germs take 
a certain time to grow in the body before the effects are seen. 
We cannot tell whether a person has a disease until after this 
incubation period is over ; hence the necessity of quarantine. 

Immunity or protection against disease may be both natural 
and acquired. The latter may be passive, through antitoxins 
introduced into the body; or active. For active immunity, the 
body works up its own resistance following the introduction of 
(a) living germs, usually attenuated ; (b) dead germs ; or (c) ex- 
tracts containing poisons made by the germs. Immunity is thus 
obtained against a number of diseases, notably diphtheria, small- 
pox, typhoid, and tetanus. Through these and other means it is 
estimated that medical science has added twelve years to the 
average life of man since the time of the Civil War. 

Problem Questions 

1. Why is quarantine a necessary precaution? 

2. Can a person have the germs of a disease in the body and still not 
show symptoms of the disease ? How might such a person be a danger to 

3. What is immunity ? What types do we have? 

4. Why are some persons more likely to take a disease than others? 

5. Why do some people have a disease more severely than others? 

6. Why does travel bring increased likelihood of disease ? 

7. How do bacteria cause disease? 


8. What is the principle underlying the antitoxin treatment for diphtheria ? 
The Schick test ? The Dick test ? 

9. What is the principle underlying vaccination against smallpox, against 
typhoid, against boils? Explain. 

10. Make a list of all germ diseases that are now treated by the passive 
method of immunity ; the active method of immunity. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Broadhurst, How We Resist Disease. J. B. Lippincott Company. 
Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 
Sharp, Foundation of Health. Lea and Febiger, 
Winslow, Healthy Living. Charles E. Merrill Company. 
Zinsser, Infection and Resistance. The Macmillan Company. 

new civ. BIOL. — 19 


Problems: What is the cause of malaria and how is it carried? 

What causes yellow fever and how is it transmitted f 

What other diseases are carried hy insects ? 

What part does the housefly take in carrying disease germs f 

What are some parasitic worms and how may we combat them? 

Laboratory Suggestions 

Demonstration. Malarial parasites in the blood corpuscles. 
Exercise. Life history of the mosquito. 
Demonstration. Trypanosomes — stained slide. 
Exercise. Life history of the house fly. 

Home project. To determine the breeding places of flies and mosquitoes in 
my neighborhood. 

Demonstration. Tapeworm and trichina (encysted). 
Demonstration. Slide showing hookworm. 

Animals as Agents of Disease. — We have already learned the 
relation of plants to disease ; it is the purpose of this chapter to 
show how animals play a part in the cause and spread of disease. 
It is obvious that the relation is twofold. An animal may be a 
parasite in man, causing certain diseases, or it may, acting as a host, 
carry a parasite for part of its life history. The malarial parasite 
and the hookworm are examples of the first type ; the mosquito, 
which carries the malarial parasite, and the flea, which transmits 
bubonic plague bacilli, are examples of the second type. 

The Cause of Malaria. — The study of the life history and the 
habits of the Protozoa has resulted in finding many parasitic 
forms, and the consequent explanation of some diseases. An 
amoeba-like parasite, of which at least three species exist, causes 
different t3TDes of malaria. This disease, not many years ago, was 
thought to be caused by bad air. (Hence the name, from Italian 
mala, bad ; aria, air.) But the work of a number of scientists 




has shown that the disease is carried by a mosquito and is caused 
by an amoeba-like organism, called plasmo'dium. When a female 
mosquito of the species anopheles (a-nof'e-lez) sucks blood 
from a person having malaria, this parasite (P in diagram) passes 
into the stomach of the mosquito. After about twelve days in 
the mosquito's body, the parasites, having passed through the 
sexual stages, establish themselves within the salivary glands of 
the mosquito. If the infected mosquito then bites a person, it 
passes the parasites into the 
human blood with its saliva. 
These parasites (A in dia- 
gram) enter the corpuscles 
of the blood, increase in 
size, and then form spores. 
The rapid process of spore 
formation results in the 
breaking down of the blood 
corpuscles and the release of 
the spores, with the poisons 
they manufacture, into the 
blood. This causes the chill 
followed by the fever so 
characteristic of malaria. 
The spores (H in diagram) 
may again enter the blood 
corpuscles and in forty- 
eight or seventy-two hours, 
depending on the kind of 
malaria, repeat the process thus described. The spores feed upon 
the red corpuscles, and destroy half or even four fifths of the 
normal number. This accounts for the pale, anemic condition of- 
a person who has malaria. The only cure for the disease is qui- 
nine in doses of from 5 to 10 grains per day. This kills the para- 
sites in the blood. 

The Malarial Mosquito. — Fortunately for mankind, not all 
mosquitoes harbor the parasite which causes malaria. The harm- 
less mosquito (culex) may be usually distinguished from the mos- 
quito which carries malaria (anopheles) by the position of the body 


Life history of the malarial parasite. Follow 
the course shown by the arrows from A back to 
A and compare with text, also from H back 


and legs when at rest. Culex lays eggs in tiny rafts of one hundred 
or more in standing water ; thus the eggs are distinguished from 
those of anopheles, which are not in rafts. Rain barrels, gut- 
ters, and old cans may breed in a short time enough mosquitoes 
to stock a neighborhood. The larvae are known as wigglers. 
They appear to hang on the surface of the water, head down, in 
order to breathe through a tube at the posterior end of the body. 

In this stage they may be rec- 
ognized by their peculiar move- 
ment when on their way to the 
surface to breathe. The pupa, 
distinguished by a large head 
and thoracic region, breathes 
through a pair of tubes on the 
thorax. The fact that both 
larvae and pupae take air from 
the surface of the water makes 
it possible to kill the mosquito 
during these stages by pouring 
oil on the surface of the water 
where they breed. The intro- 
duction of minnows, gold fish, 
or other small fish which feed 
upon the larvae in the water 
where the mosquitoes breed 
will do much in freeing a neigh- 
borhood from this pest. Drain- 
ing swamps or low land which 
holds water after a rain is an- 
other method of extermination. Some of the mosquito-infested 
districts around the city of New York have been almost freed 
from mosquitoes by draining the salt marshes. Long shallow 
trenches are so built as to tap and drain off any standing water 
in which the eggs might be laid. In this way the mosquito has 
been almost exterminated along some parts of our New England 

Since the beginning of historical times, malaria has been preva- 
lent in regions infested by mosquitoes. The ancient city of Rome 

Life history of two mosquitoes — at 
the left, culex ; at the right, anopheles, the 
malarial mosquito. Note the four stages 
of each — eggs, larva, pupa, adult. 



was so greatly troubled by periodic outbreaks of malarial fever 
that a goddess of fever came to be worshiped in order to lessen the 
severity of what the inhabitants believed to be a divine visitation. 
At the present time the malaria of Italy is being successfully fought 
and conquered by the draining of the mosquito-breeding marshes. 
In Arkansas, Mississippi, and other Southern states successful 
fighting of malaria by drain- 
ing marshes, oiling standing 
water, and screening houses 
has greatly reduced the 
number of malaria patients. 

Yellow Fever and Mos- 
quitoes. — Another disease 
carried by mosquitoes is 
yellow fever. In the year 
1878 there were 125,000 
cases and 12,000 deaths in 
the United States, mostly 
in Alabama, Louisiana, and 
Mississippi. During the 
French attempt to con- 
struct the Panama Canal, 

the work was at a standstill part of the time because of the ravages 
of yellow fever. Before the war with Spain, thousands of people 
were ill in Cuba. But to-day yellow fever has almost disappeared, 
both there and in the Canal Zone, through proper control of the 
fever-carrying mosquito aedes (a-e'dez ; formerly called stegomy'ia). 

The knowledge that aedes carries the parasite that causes yellow 
fever is due to the experiments during the summer of 1900 of a 
commission of United States army officers, headed by Dr. Walter 
Reed. Of these men one. Dr. Jesse Lazear, lost his life in an 
experiment — to prove that yellow fever is carried by mosquitoes. 
He allowed himself to be bitten by a mosquito that was known 
to have bitten a yellow fever patient, contracted the disease, and 
died a martyr to science. Others, soldiers, volunteered to test 
further by experiment how the disease was spread, so that in the 
end Dr. Reed was able to prove that if the aedes mosquito could 
be prevented from biting people who had yellow fever, the disease 


w^ .. 1 


'■*'^^W^^^ ^^ 

The best way to prevent a swamp irom breed- 
ing mosquitoes is to drain it. 


250 SOO 750 1000 IZ50 ISOO 










could not be spread. The accompanying illustration shows the 
result of this discovery for the city of Havana. For years Havana 
was considered one of the pest spots of the West Indies. Visitors 
shunned this port and commerce was much affected by the con- 
stant menace of yellow fever. At the 
time of the American occupation after 
the war with Spain, the experiments 
referred to above were undertaken. 
The city was cleaned up, proper sani- 
tation introduced, screens placed in 
most buildings, and the breeding places 
of the mosquitoes were so nearly de- 
stroyed that the city was practically free 
from mosquitoes. The result, so far as 
yellow fever was concerned, was star- 
tling, as you can see by reference to the 
chart. It was eighteen years after the 
discovery of the carrier of yellow fever 
that its cause was discovered by Dr. 
Noguchi (no'goo-cHe) of the Rockefeller 
Institute. This is a one-celled organ- 
ism — a spirochcete (spi-r6-ke'te) — so 
small as to escape detection except 
under the most powerful microscope. 
Dr. Noguchi has prepared a vaccine 
and a serum, both of which have been 
used with great success in South 
America under the auspices of the 
Rockefeller Institute.^ 
Other Protozoan Diseases. — Many other diseases of man are 
probably caused by parasitic protozoa. Dysentery of one kind 
appears to be caused by the presence of an amoeba-like animal 
{entamoeha) in the digestive tract. Rabies, possibly smallpox, 
and other diseases are caused by protozoa. Relapsing fever and 
the dread disease syphilis are caused by spirochsetes, organisms 
which look like the spirillum. 









1/8 Carrier of yellow fever discovered 



1 24 First Cuban rule 



Notice the difference in the 
number of yearly deaths from 
yellow fever before and after the 
American occupation of Havana. 

^ See Eighth Annual Report of the International Health Board of the Rocke- 
feUer Institute, 1921. 


Another group of protozoan parasites are called tryp'anosomes. 
These are parasitic in insects, fish, reptiles, birds, and mammals 
in various parts of the world. They cause several diseases of 
cattle and other domestic animals, being carried to the animal in 
most cases by flies. One of this family is believed to live in the 
blood of native African zebras and antelopes. Seemingly it 
does them no harm, but if one of these parasites is transferred by 
the dreaded tsetse (tse'tse) fly to one of the domesticated horses 
or cattle of that region, death of the animal results. 

Another fly carries to the natives of Central Africa a species of 
trypanosome which causes " the dreaded and incurable sleeping 
sickness." This disease has carried off more than fifty thousand 
natives yearly, and many Europeans have succumbed to it. Its 
ravages are largely confined to an area near the large Central Afri- 
can lakes and the upper Nile, for the fly which carries the disease 
lives near water, seldom going more than 150 feet from the banks 
of streams or lakes. The British government has attempted 
to control the disease in Uganda by moving all the villages at 
least two miles from the lakes and rivers. Among other diseases 
that may be due to protozoa is kala-agar, a fever in hot Asiatic 
countries which is probably carried by the bedbug, and African 
tick fever, carried by a small insect called the tick. The body 
louse carries the dreaded typhus fever, which has played great 
havoc in Russia and the near East since the World War. Bubonic 
plague, one of the most dreaded of all bacterial diseases, is carried 
to man by fleas from rats or ground squirrels. In this country 
many fatal diseases of cattle, as '' tick fever," or Texas cattle 
fever, are caused by protozoa. 

The House Fly. — We have already seen that mosquitoes of 
different species carry malaria and yellow fever. Another addition 
to the black list is the house fly or typhoid fly. The development 
of the house fly is extremely rapid. A female may lay from one 
hundred to two hundred eggs. These are usually deposited in 
filth or manure. Dung heaps about stables, privy vaults, ash 
heaps, uncared-for garbage cans, and fermenting vegetable refuse 
form the best breeding places for flies. In warm weather, the 
eggs hatch a day or so after they are laid and the larvae or maggots 
crawl out. After about one week of active feeding these wormlike 


maggots become quiet and go into the pupal stage, whence under 
favorable conditions they emerge within less than another week 
as adult flies. The adults breed at once, and in a short summer 
there may be over ten generations of flies. This accounts for the 


Four stages in the complete metamorphosis of the house fly. 

great number. Fortunately, relatively few flies survive the winter. 
The membranous wings of the adult fly appear to be two in number, 
^ second pair being reduced to tiny knobbed hairs called balancers. 
The head is freely movable, with large compound eyes. The 
mouth parts form a proboscis, which is tonguelike, the animal 
obtaining its food by lapping and sucking. The foot shows a 
wonderful adaptation for clinging to smooth surfaces. Two or 
three pads, each of which bears tubelike hairs that secrete a sticky 

fluid, are found on its under 
surface. It is by this means 
that the fly is able to walk 
upside down, and carry 
bacteria on its feet. 

The House Fly a Disease 
Carrier. — The common fly 
is recognized everjr^here as 
a pest. Flies have long been 
known to spoil food through 
their filthy habits, but it is 
only recently that they 
have been blamed for 
spreading several diseases 
caused by bacteria. It 
has been found that a single fly might carry on its feet anywhere 
from 500 to 6,600,000 bacteria, the average number being over 
1,200,000. Not all of these germs are harmful, but they might 

Foot of a house fly, highly magnified. 


Colonies of bacteria which have devel- 
oped in a culture medium upon which a 
fly was allowed to walk. 

easily include those of typhoid fever, tuberculosis, '' summer 

complaint," and possibly other diseases. A pamphlet published 

by the Merchants' Association 

in the city of New York shows 

that the rapid increase of flies 

during the summer months has 

a definite correlation with the 

increase in the number of cases 

of '' summer complaint." Ob- 
servations in other cities seem 

to show the increase in number 

of typhoid cases in the early fall 

is due, in part at least, to the 

same cause. A terrible toll of 

disease and death may be laid 

at the door of the typhoid fly. 
Control. — Cleanliness which 

destroys the breeding places of 

flies, the frequent removal and destruction of garbage, rubbish, and 

manure, covering all food when not 
in use, and especially the careful 
screening of windows and doors 
during the breeding season are wise 
precautions to prevent diseases. 
Far more important than to " swat 
the fly " is to " remove their breed- 
ing places " ! 

Other Insect Disease Carriers. — 
Fleas and bedbugs recently have 
been added to. those insects proved 
to carry disease to man. Bubonic 
plague, which is primarily a disease 
of rats, is undoubtedly transmitted 
from infected rats to man by fleas. 
Fleas are also believed to transmit 
leprosy, although this is not proved. 
To rid a house of fleas we must first find their breeding places. 

Old carpets, the sleeping places of cats or dogs, and any dirty 

















































There were 329 typhoid cases in a 
city of about 50,000 inhabitants in 
1910, 158 in 1911, 87 in first 10 
months of 1912. 80 to 85 per cent 
of outdoor toilets were made fly proof 
during the winter of 1910. Account 
for the decrease in typhoid after 
the flies were kept out of the toilets. 


unswept corner may hold the eggs of the flea. The young breed in 
cracks and crevices, feeding upon organic matter there. Eventu- 
ally they come to live as adults on their warm-blooded hosts : cats, 
dogs, and man. Evidently destruction of the breeding places, 
careful washing of all infected areas, the use of a creosote prepara- 
tion in crevices where the larvae may be hidden, are the most effec- 
tive methods of extermination. Pets which might harbor fleas 
should be washed frequently with a weak (two to three per cent) 
solution of creolin. It is thought probable that bedbugs spread 
typhus and relapsing fevers. They prefer human blood to other 
food and live in bedrooms because this food can be obtained 
there. They are extremely difficult to exterminate because their 
flat bodies allow them to hide in cracks out of sight. Wooden 
beds are thus better protection for them than iron or brass beds. 
Boiling water poured over the cracks where they breed, or a mix- 
ture of four parts of strong corrosive sublimate with four parts of 
alcohol and one part of spirits of turpentine is an effective remedy. 

Bdcillus pesfis 

Diagram showing how bubonic plague is carried to man. 

Animals Other than Insects may be Disease Carriers. — The 

common brown rat is an example of a mammal, harmful to civilized 
man, which has followed in his footsteps all over the world. Start- 
ing from China, it spread to eastern Europe, thence to western 
Europe, and in 1775 it had arrived in this country. In seventy- 
five years it reached the Pacific coast and it is now fairly common 
all over the United States, being one of the most prolific of all 
mammals. Rats carry bubonic plague, the '^ Black Death '^ 
of the Middle Ages, a disease estimated to have killed 25,000,000 
people during the fourteenth century. Plague is primarily a dis- 
ease of rats. Fleas bite the rat and then transmit the disease to 



man. In 1900 the plague gained entrance on our western coast. 
It killed more than 100 persons during the next four years, and has 
broken out occasionally since. The ground squirrels of California 
have become infected with the plague, doubtless from the rats 
which live in their burrows, so now the danger of other outbreaks 
of the plague will be present until the ground squirrels are exter- 
minated. Over a million rats were killed in fighting the last plague 
outbreak in California and efforts are being made in all large cities 
to eradicate this pest. 

Other Parasitic Animals cause Disease. — Besides parasitic 
protozoa other forms of animals have been found that cause 
disease. Chief among these are certain round and flat worms, 
which live as parasites not only on man but on many animals and 
plants. A one-sided relationship has thus come into existence 
where the worm receives its living from the host, as the animal 
which maintains the parasite is called. Consequently the parasite 
frequently becomes fastened to its host during adult life and is 
reduced to a mere bag through which the fluid food prepared by its 
host is absorbed. Sometimes a complicated life history results 
from parasitic habits. Such is the life history of the liver fluke, 
a flat worm which kills sheep (page 228), and of the tapeworm. 

tian eats 
underdone pork 


Cyst in muscle 
of pig 

The tapeworm may spend part of its life cycle in a mammal other than man, or in 
a fish, and be taken with improperly cooked food into the human body, where it may 
become a parasite. 

Ces'todes or Tapeworms. — ^ These parasites infest man and many 
other vertebrate animals. One tapeworm {Tcenia solium) passes 
through two stages in its life history, the first within a pig, the sec- 
ond within the intestine of man. The developing eggs are passed 
off with wastes from the intestine of man. The pig, an animal with 
dirty habits, may take in the tapeworm embryos with its food. 


These develop within the intestine of the pig, but soon make their 
way into the muscles or other tissues, where they are known as 
bladder worms. If man eats undercooked pork containing them, 
he is likely to become a second host for tapeworms. Another 
common tapeworm parasitic on man {Tmnia saginata) lives part 
of its life as an embryo within the muscles of cattle. The adult 
tapeworm consists of a round headhke part provided with hooks, 
by means of which it fastens itseK to the wall of the intestine 
(figure on page 240) . This head now buds off a series of segment- 
Hke structures, which are practically bags full of sperms and eggs. 
These structures, caUed proglot'tids, break off from time to time, 
thus allowing the developing eggs to escape. The proglottids 
have no separate digestive systems, but the whole body surface, 
bathed in digested food, absorbs it and is thus enabled to grow 

Roundworms. — Still other wormlike creatures called round- 
worms are of importance to man. Some, as the vinegar eel found 
in vinegar, or the pinworms parasitic in the lower intestine, partic- 
ularly of children, do httle or no harm. The as'caris, a larger 
roundworm, sometimes infests children but is rarely dangerous to 
its host. 

The pork worm or trichina (tri-ki'na), however, is a parasite 
which may cause serious injury. It passes through the first 
part of its existence as a parasite in a pig or other vertebrate 
(cat, rat, or rabbit) ; it is covered within a tiny sac or cyst, in the 
muscles of its hosts (figure on page 240). If undercooked pork 
containing these cysts is eaten by man, the covering is dissolved 
off by the action of the digestive fluids, and the living trichina 
becomes free in the intestine of man. Here it reproduces, deposit- 
ing the young on the other side of the intestinal wall; and the 
young migrate into muscles, causing inflammation there and 
resulting in a painful and often fatal disease known as trichino'sis. 
The government inspects all animals killed for food in large 
slaughterhouses, so that there is little likelihood nowadays of 
becoming infected with trichina. Pork from private slaughter- 
houses may be infected, however, so it is safer to cook pork 
thoroughly, so that any parasites will be killed before the meat 
is eaten. 



FilaWia are small roundworms that cause various tropical dis- 
eases — the most serious of which is elephanti'asis. The parasites 
possibly enter the body in drinking water and some are probably 
introduced by the bite of a mosquito. 

The Hookworm. — The account of the discovery by Dr. C. W. 
Stiles of the Bureau of Animal Industry, that the laziness and shift- 
lessness of the " poor whites " of the South 
is partly due to a parasite called the hook- 
worm, reads like a fairy tale. 

The people, largely farmers, become in- 
fected with a larval stage of the hookworm, 
which develops in moist earth. It enters 
the body usually through a break in the 
skin of the feet, for children and adults 
alike, in certain localities where the disease 
is cormnon, go barefoot to a considerable 

A complicated journey from the skin to 
the intestine now follows. The larvae pass 
through the veins to the heart, from there 
to the lungs, where they bore into the air 
passages, and eventually reach the intestine 
by way of the throat. One result of the 
injury to the lungs is that many thus in- 
fected are subject to tuberculosis. The 
adult hookworms, once in the food tube, 
fasten themselves to the walls, which they 
puncture; and then they feed upon the 
blood of their host. The loss of blood from 
this cause is not sufficient to account for 
the bloodlessness of the person infected, but 
it has been discovered that the hookworm 
pours out into the wound a poison which 
prevents the blood from clotting rapidly 
(see page 164) ; hence a considerable loss 
of blood occurs from the wound after the 
hookworm has finished its meal and gone to another part of 
the intestine. 

Hookworm, highly 
magnified, and diagram 
of course followed from 
foot to heart, to lungs, to 
throat, to intestine. Ex- 
plain from text. 


The prevention of hookworm hes in sanitary toilets and in 
proper covering for the feet. The remedy for the disease is very 
simple : thymol, which weakens the hold of the hookworm, 
followed by Epsom salts. 

A family suffering from hookworm disease. Proper treat- 
ment freed them from more than 10,000 hookworms. After 
they were cured, the father raised a big crop of cotton and got 
out of debt ; and the children made good progress in school. 

For years a large area in the South undoubtedly has been 
retarded in its development by this parasite ; hundreds of millions 
of dollars have been wasted and thousands of lives have been 
needlessly sacrificed. The Rockefeller Foundation has made a 
study of conditions all over the world and finds that in almost all 
semitropical countries the hookworm is present and that in some 
parts of the world almost all the people are infected. 

''The hookworm is not a bit spectacular: it doesn't get itself discussed 
in legislative halls or furiously debated in political campaigns. Modest and 
unassuming, it does not aspire to such dignity. It is satisfied simply with 
(1) lowering the working efficiency and the pleasure of living in something like 
two hundred thousand persons in Georgia and all other Southern states in 
proportion ; with (2) amassing a death rate higher than tuberculosis, pneu- 
monia, or typhoid fever ; with (3) stubbornly and quite effectually retarding 
the agricultural and industrial development of the section ; with (4) nullifying 
the benefit of thousands of dollars spent upon education ; with (5) costing the 
South, in the course of a few decades, several hundred millions of dollars. 
More serious and closer at hand than the tariff ; . . . making the menace of 
the boll weevil laughable in comparison — it is preeminently the problem of 
the South."- — Atlanta Constitution. 


Summary. — In this chapter we have found that a part of the Kfe 
history of the malarial parasite is spent in the red blood corpuscles 
of man and that its sexual stages are passed in the body of the 
anopheles mosquito, thus making it necessary for the parasite to 
have two hosts in order to complete its life history. Yellow fever is 
caused by a parasite which is transferred to man by the mosquito 

The house fly is found to be a disease carrier, also the flea, body 
louse, and probably the bedbug. 

The parasitic worms that are most serious enemies of man are 
the tapeworm, trichina, and hookworm. The last named is one 
of the largest economic problems in the tropics. 

Problem Questions 

1. In what ways do animals affect man ? 

2. Show how malaria is transmitted. How is it caused ? What conditions 
must exist in order that it be transmitted ? 

3. What are three ways to exterminate mosquitoes from a locality? 

4. Is it possible to do awaj^ with malaria ? May the same be said of yellow 
fever ? 

5. How is yellow fever spread ? How can the diseass be fought successfully ? 

6. What other diseases are insect-carried? 

7. What different kinds of organisms cause disease? 

8. How would you fight the fly pest in your home ? In your town ? 

9. What are the best means of exterminating the rat? (Look up Lantz's 
report, Farmers' Bulletin 396.) 

10. Describe the method of hookworm infection and the method of cure. 
How can we rid the world of hookworm disease ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 
Folsom, Entomology. P. Blakiston's Son and Company. 
Hunter and Whitman, Civic Science in the Community. American Book 

Marshall, Microbiology. P. Blakiston's Son and Company. 
Reese, Economic Zoology. P. Blakiston's Son and Company. 
Winslow, Healthy Living. Charles E. Merrill Company. 
Farmers' Bulletins 33, 369, 444, 569, 670, 734, 896, 1057, 1354, 1408. 
Public Health Reports. Supplement 29, 569. 
United States Dept. of Agriculture. Bulletins 132, 260. 
United States Bureau of Fisheries. Economic Circular 17. 


Problems: How may we improve our conditions at home? 
How may we help improve our conditions at school f 
How does the community care for the improvement of our environ- 

(a) By the inspection of buildings. 
(h) By the inspection of food supplies, 
(c) By the inspection of milk, 
{d) By the care of water supplies. 
(e) By the disposal of wastes. 
(J) By the care of public health. 

Laboratory Suggestions 

Home exercise. How to ventilate my bedroom. 

Demonstration. Effect of the use of a duster and a damp cloth upon 
bacteria in the schoolroom. 

Home project. A comparison of luncheon dietaries. 

Home project. A sanitary survey of the conditions of my block or an area 
of my town. 

Demonstration. The bacterial content of milk of various grades and 
from different sources. 

Demonstration. The bacterial content of distilled water, rain water, tap 
water, dilute sewage. 

Laboratory exercise. Plotting of curves from board of health tables to show 
the mortality from certain diseases during certain times of year. 

Project. A study of the work of the local board of health. 

The Purpose of this Chapter. — In the preceding chapters we 
have traced the lives of both plants and animals within their own 
environments. We have seen that man, like them, needs a favor- 
able environment in order to live in comfort and health. It will 
be the purpose of the following pages first to show how we as indi- 
viduals may improve our home environment, and second, to see 




how we may aid the civic authorities in improving the conditions in 
the community in which we hve. 

Home Surroundings : The Bedroom. — As we spend about one 
third of our time in our bedrooms, we should give them more than 
passing attention. A bedroom should have good ventilation 
obtained by two sunny windows if possible, or by a window open 
both at top and at bottom. An ideal arrangement includes a 
sleeping porch (page 185), with the bedroom used as a dressing 
room and study. Such a condition as this is manifestly im- 
possible for most people in a crowded city, where too often the 
apartment bedrooms open upon narrow and ill- ventilated courts. 

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This map shows how cases of tuberculosis recur in the same locality and in the same 
houses year after year. Each black dot represents one case of tuberculosis. 

Until comparatively recent times, many tenement houses were 
built so that the bedrooms had very little light or air; now, 
thanks to good laws, wide airshafts and larger windows are re- 
quired. Model laws require that every room in an apartment 
except the bathroom must have at least 90 square feet floor area, 
that every room must have at least one outside window, and that 
at least 25% of a lot (except the corner) should not be built 

Care of the Bedroom. — Bedroom furniture should be light and 
easy to clean, the bedstead of iron, and the floor painted or of 
hardwood. Heavy hangings and carpets which collect dust should 
be avoided. Rugs on the floor may easily be removed and cleaned. 
The furniture and woodwork should be wiped with a damp cloth 
every day, for bacteria soon settle with dust on every horizontal 

H. NEW CIV. BIOL. — 20 


surface. Dusting with a dry cloth simply stirs up the bacteria 
and does not remove them. In certain city tenements tuberculosis 
is believed to have been spread by people occupying rooms in which 
a previous tenant had tuberculosis. A new tenant should insist 
on a thorough cleaning of the bedrooms and removal of old wall 
paper before occupancy. 

Sunlight and Dry Soil Important. — A house in the country as 
well as an apartment in the city should have sunlight in at least 
some of the rooms. A location in which damp soil or marshy pools 
are found is not healthful. Mosquitoes may breed there, and the 
wet soil may become water-soaked and foul-smelling. Cellars of 
houses in such localities are bound to be damp and musty, mold 
abounds, and it becomes difficult to keep food in damp cellars. 

Heating. — Houses in the country are often heated by open 
fires, stoves, or hot-air furnaces, all of which make use of heated 
currents of air to warm the rooms. But in city apartments, 
usually, pipes conduct steam or hot water from a central plant to 
the rooms and warm over the stale air without providing a fresh 
supply of air. Hot water gives a more even heat than steam but is 
expensive to install. Some system which introduces warmed /res/i 
air is especially desirable. 

Artificial Lighting. — Lighting of our rooms is a matter of much 
importance. A student lamp, or shaded incandescent light, should 
be used for reading, so that the eyes are protected from direct light. 
Gas is a dangerous servant, because it contains a very poisonous 
substance, carbon monoxide. ^' It is estimated that 14 per cent 
of the total product of the gas plant leaks into the streets and 
houses of the cities supplied." This forms an unseen menace to 
health in cities. Gas pipes, especially gas cocks, should be watched 
carefully for escaping gas. Worn and leaky rubber tubing should 
not be used to conduct gas to movable lamps. 

Care of Foods. — Although we can buy many foods in sealed 
packages, much of our food is exposed to the handling of people 
who may be careless. Vegetables and meats are too often exposed 
to dust, dirt, and handling. We should patronize only the butcher 
who keeps his meat iced in covered counter cases and whose helpers 
show clean habits in handling and delivering foods. Our grocer 
should keep fresh vegetables and fruits covered during the summer 


months, as a protection from flies. Raw fruits and vegetables 
should be carefully washed before being eaten. 

Care of Dishes. — Home life for some people is ^' an endless 
washing of dishes." But carelessness in dishwashing may mean 
the spreading of disease. Dr. Broadhurst of Teachers College, 
New York, recently made a series of tests with several hundred 
glasses and cups smeared with saliva and found that hand washing 
without rinsing does not remove all the bacteria. Some of the 
bacteria are not destroyed unless boiling hot water is used. Dishes 
should first be washed with hot, soapy water, then dipped in a sec- 
ond pan of boiling hot water, and finally wiped with a clean, dry 
towel. At the time of the influenza epidemic during the World War 
an investigation was made of 66,000 men, half of whom ate from 
plates which were washed in boiling water, the other half from 
mess plates which were washed carelessly by the men. The influ- 
enza rate was 51 per 1000 among the men who ate from properly 
washed dishes and 252 per 1000 among the men who ate from mess 
plates. These facts show plainly the need of proper washing of 

Insects and Foods. — In the summer our houses should be pro- 
vided with screens. All food should be carefully protected from 

During the summer all food should be protected from flies. Why? 

flies. Dirty dishes, scraps of food, and garbage should be quickly 
cleaned up and disposed of after a meal. Insect powder (pyr- 
ethrum) will help keep out ^' croton bugs " and other undesirable 
household pests, but cleanliness will do far more. Most kitchen 


pests, such as the roach, staj^ onh^ where thej^ find dirt and food 

Use of Ice. — Food should be properly cared for at all times. 
During the summer, especially where children live, iceboxes are a 
necessity, in order to keep milk fresh. Experiments made with 
good fresh milk, which at the first observation contained about 
30,000 bacteria per ctibic centimeter, showed that twent^^-four hours 
later, if kept at the tem- 

perature of the average 
icebox (about 50° Fahren- 
heit) there were about the 
same nmnber of bacteria 
present ; while some of the 
same milk exposed to a 
temperature of 68° Fah- 
renheit showed 500,000,000 
bacteria to the cubic centi- 

Home Water Supplies. 
— We have already learned 
why water which comes 
from a shallov\' well or im- 
protected spring should be 
carefull}^ tested and pro- 
tected against pollution. 
City water supplies like- 
wise need to be tested at 
regular intervals. Ice to 
be used in drinking water 
should be carefulh^ washed, for experiments show that although 
nearly all bacteria in ice are killed after storage of a few weeks, yet 
some disease germs are occasionall}^ found on the outside of pieces 
of ice because of careless handling. Water coolers and filters are 
usually traps for bacteria and are often dangers rather than aids in 
sanitary living. ^Moreover, a water cooler in a house usually is 
accompanied by a common drinking cup, which is imsanitary. 

Disposal of Wastes. — In country homes where cesspools receive 
human wastes, care should be used in selecting their location and 

Tne wrong and the right kind of garbage cans. 



in cleaning. A septic tank costs little more to install and is much 
safer than the ordinary cesspool. In city houses the disposal of 
human wastes is provided for by a system of sewers. Garbage 
should be disposed of each day. The garbage pail should be fre- 
quently sterilized by rinsing it with boiling water and plenty of 
lye or soap. Remember that flies frequent the uncovered garbage 
pail, and that they may fly from it to your food. Collection and 
disposal of garbage is the work of the municipality. 

School Surroundings ; how to improve them. — From five to 
six hours a day for forty weeks a year are spent by the average boy 

The culture (A) was exposed to the air of a dirty street in the crowded part of 
Manhattan. (B) was exposed to the air of a well-cleaned and watered street in 
the uptown residence portion. Which culture has the more colonies of bacteria? 
How do you account for this ? 

or girl in the schoolroom. It is part of our environment and should 
therefore be considered as worthy of our care. A schoolroom 
should be not only attractive, but also clean and sanitary. City 
schools, because of their location, the sometimes poor janitor 
service, and especially the selfishness and carelessness of children 
who use them, may be very dirty and unsanitary. Dirt and dust 
breed and carry bacteria. Plate cultures show that there are 
greatly increased numbers of bacteria in the air when pupils are 
moving about, for then dust, bearing bacteria, is stirred up and 
circulated through the air. Sweeping and dusting with dry 
brooms or feather dusters only stirs up the dust, leaving it to settle 


in some other place with its load of bacteria. Professor Hodge 
tells of an experience in a school in Worcester, Mass. A health 
brigade was formed among the children, whose duty was to clean 
the rooms every morning by wiping all exposed surfaces with damp 
cloths. In a school of 425 pupils not a single case of communi- 
cable disease appeared during- the entire year. Why not try this 
in your own school? 

Unselfishness the Motto. — Pupils should be unselfish in the 
care of a school building. Papers and scraps dropped by some 
careless boy or girl make the surroundings unpleasant for hundreds 
of others. Chalk thrown by some mischievous boy and then 
tramped underfoot causes dust particles in the air, which may 
irritate the lungs of a hundred innocent schoolmates. Colds 
may be spread by spitting in the halls or on the stairways. 

Lunch Time and Lunches. — If you bring your lunch to school, 
it should be clean, tasty, and well balanced as a ration. In most 
large schools lunch rooms are part of the equipment, and balanced 
lunches can be obtained at low cost. Do not make a lunch entirely 
from cold food, if hot can be obtained. Do not eat only sweets. 
Ice cream is a good food, if taken with something else, but be sure 
of the quality of your ice cream. More than 250 samples of ice 
cream collected in Washington, D. C, ranged from 37,500 to 
365,000,000 bacteria per cubic centimeter, the condition of the ice 
cream depending on the sanitary condition of the place where it 
was manufactured. Above all, be sure the food you eat is clean. 
Stands on the street, exposed to dust and germs, often have for 
sale food that is far from fit for human consumption. 

If you eat your lunch on the street near your school, remember 
not to scatter refuse. Paper, bits of lunch, and the like, scattered 
on the streets around your school, show lack of school spirit and 
lack of civic pride. Let us learn above all other things to be good 

Inspection of Factories, Public Buildings, etc. — It is the duty 
of a city to inspect the condition of all public buildings and espe- 
cially of factories. Inspection should include the supervision of 
the work undertaken. Certain trades where grit, dirt, or poison- 
ous fumes are given off are dangerous to health; hence care for 
the workers becomes a necessity. There are other occupations 



where noise or monotony of work or too rapid movement causes 
fatigue and more frequent accidents. Workmen in such trades 
must be protected, and many state laws now provide for proper 
gas masks, wheel and belt protectors, lighting and other devices 
that protect workmen from the particular hazard to which they 
are exposed. Factories should also be inspected as to cleanliness, 
the amount of air space per person employed, ventilation, toilet 
facihties, and proper fire protection. Tenement inspection should 
be thorough and should 
aim to provide safe and 
sanitary homes. 

Inspection of Food Sup- 
plies. — In a city certain 
regulations for the care of 
public food supplies are 
necessary. Inspectors are 
appointed to see that the 
laws are enforced and that 
foods are protected for the 
thousands of people who 
are to use them. All raw 
foods exposed on stands 
should be covered so as to 
prevent insects or dust 
laden with bacteria from 
coming in contact with 
them. Meats must be in- 
spected for diseases, such as tuberculosis in beef, or trichinosis in 
pork. Inspection of cold storage plants, of factories where foods 
are canned, and of bakeries must be part of the work of a city in 
caring for its citizens. 

Care of Raw Foods. — It is well for us to remember that fruits 
and vegetables can be carriers of disease, especially if they are sold 
from exposed stalls or carts and handled by the passers-by. They 
should be carefully pared or washed before being used. Spoiled 
or over-ripe fruit, as well as meat which is decayed, is swarming 
with bacteria and should not be used. 

An interesting exercise would be the inspection of conditions 

Eye protectors made of glass and placed over 
grinding wheels. Other shields to prevent ac- 


in your own home block or in the town in which you Hve. Make a 
map showing the buildings. Locate all houses, stores, factories, 
etc. Indicate any cases of communicable disease on the map. 
Mark all heaps of refuse in the street, all uncovered garbage 
pails, any street stands or push carts which sell uncovered fruit, 
and any stores which have an excessive number of flies. A sani- 

^Imerican Aluscum oj Natural History, 

Push cart with glass covers to protect fruit from dust and flies. 

tary survey made by the biology class may bring up a number of 
vital topics not mentioned here and may be of great value in 
pointing out certain defects or merits of your community. 

Care in Production of Milk. — Milk drawn from a healthy cow 
should be nearly free from bacteria. But immediately on reaching 
the air it may receive bacteria from the air, from the hands of th 
person who milks the cow, from the pail, or from the cow herself. 
Cows should, therefore, be milked in surroundings that are sani- 
tary (figure on page 4), the milkers should wear clean garments, 
put on over their ordinary clothes at milking time, and pails and all 
utensils used should be kept clean. Especially the surface exposed 
on the udder from which the milk is drawn should be cleansed before 



Most large cities now send inspectors to the farms from which 
milk is supplied. Cards are used which score the health of the 
cows, the cleanliness of their surroundings, the health of the work- 
ers, the care and construction of the utensils, and the methods of 
handling the milk. Farms that do not accept certain standards 
of cleanliness are not allowed to have their milk become part of 
the city supply. 

Tuberculosis and Milk. — Many dairy herds in this country are 
infected with tuberculosis. It is also known that the tubercle 
bacillus of cattle causes 
some kinds of tuberculosis 
in young children. Fortu- 
nately, the tuberculosis 
germ does not grow in milk, 
so that even if milk from 
tuberculous cattle should 
get into our supply, it 
would be diluted with the 
milk of healthy cattle. In 
order to protect our milk 
supply from these germs it 
would be necessary to kill 
all tubercular cattle or to 
pasteurize the milk so as to 
kill the germs in it. 

Other Disease Germs in 
Milk. — We have already 
learned how typhoid may 
be spread througii milk. 
Usually such outbreaks of 
typhoid may be traced to 
a single case of the disease, 
often a person who is a 'Hy- 
phoid carrier," i.e. one who 

is not suffering from the effects of the disease but who carries the 
germs in his body. Sometimes the milk cans may be washed in 
contaminated water or the cows get the germs on their udders 
by wading in a polluted stream. Diphtheria, septic sore throat. 






1 1 1° • 1 r • -1 r 


Typhoid may be spread in a city through 
an infected milk supply. The black spots 
mean cases of typhoid. A, a farm where ty- 
phoid exists. The dashes in the streets repre- 
sent milk routes. B, a second farm which 
sends part of its milk to A. The milk canf3 
from B are washed at farm A and sent back 
to B. A few cases of typhoid appear along 
j5's milk route. How do you account for 


scarlet fever, and Asiatic cholera are also undoubtedly spread 
through milk supplies. 

Grades of Milk in a Community Supply. — Milk which comes to 
a community must have certain standards which have been set by 
state and city boards of health and by various medical bodies. 
These standards are chemical and bacteriological. The United 
States Public Health Service suggests the following standards for 
state adoption : 

Milk must have at least 3% butter fat, must have at least 11.5% 
solids, and must not be diluted or adulterated. 

The cows must be tested at least once a year for tuberculosis 
and must be in good physical condition when used for milk pro- 
duction. The milk and dairy conditions and methods of handling 
must be scored from time to time. 

Milk must be graded as follows : 

Grade A Milk (Raw) must come from dairies that score at least 
75%, and the milk must not contain more than 100,000 bacteria 
to the cubic centimeter at the time of delivery. 

Grade A Milk (Pasteurized) must come from dairies that score 
at least 70% and the milk must not contain over 200,000 bacteria 
to the cubic centimeter before pasteurization, nor more than 
30,000 at the time of delivery to consumer. 

Grade B Milk (Raw) must come from dairies that score at least 
60% and must not contain more than 300,000 bacteria to the cubic 

Grade B Milk (Pasteurized) must come from dairies that score 
at least 55% and must not contain more than 1,000,000 bacteria 
per cubic centimeter before pasteurization nor more than 100,000 
per cubic centimeter at time of delivery to consumer. 

Milk sold in bulk and exposed to dust is unfit for any purpose 
except cooking. It should under no circumstances be given to 
children. A regulation was made by the Department of Health 
of the city of New York that milk sold " loose " in restaurants, 
lunch rooms, soda fountains, and hotels must be pasteurized. 

Care of a City Milk Supply. — Besides caring for milk in its 
production on the farm, proper transportation facilities must be 
provided. Some of the milk used in Boston, Chicago, and New 
York is forty-eight hours old before it reaches the consumer. Milk 


used in the last-named city is said to come from eight states and 
from Canada. During shipment it must be kept in refrigerator 
cars, and during transit to customers it should be iced. Why? 
All but the highest grade milk should be pasteurized. Why? 
Milk should be bottled by machinery, if possible, to insure no 
personal contact ; it should be kept in clean, cool places ; and no 
milk except that which is to be used for cooking should be sold 
by dipping from cans. Why is this method of dispensing milk 
likely to make it impure ? 

Care of Milk in the Home. — Finally, milk at home should re- 
ceive the best of care. It should be kept on ice and in covered 
bottles, because it readily takes up the odors of other foods. If 
we are not certain of its purity or keeping qualities, it should be 
pasteurized at home. Why? 

Water Supplies. — One of the greatest assets to the health of a 
large city is pure water. By pure water we mean water free from 
all organic impuritieS; including germs. Water from springs and 
deep driven wells is the safest water ; that from large reservoirs 
next best ; while water that has drainage in it, river water for 
example, is very unsafe unless properly treated. 

The water from deep wells or springs, if properly protected, will 
contain few bacteria. Water taken from shallow, unprotected 
wells has from 100 to 20,000 bacteria per cubic centimeter. Water 
taken from protected streams into which no sewage flows has but 
few bacteria (from 50 to 300 bacteria per cubic centimeter), and 
these are destroyed if exposed to the action of the sun and the con- 
stant aeration (mixing with oxygen) which the surface water 
receives in a large lake or reservoir. But water taken from a river 
into which the sewage of towns and cities flows may contain many 
hundreds of thousands of bacteria to the cubic centimeter, and 
must be filtered and chlorinated before it is fit for use. 

Typhoid fever germs live in the intestine, hence the excreta of 
a typhoid patient contain large numbers of typhoid germs. In a 
city such germs might eventually pass from the sewer into a river 
or a lake. Many cities take their w^ater supply directly from 
rivers, sometimes not far below another large town. Such cities 
must take many germs into their water supply. Many cities, as 
Cleveland and Buffalo, take their water from lakes into which 


their sewage flows. Others, as Albany, Pittsburgh, and Phila- 
delphia, take their drinking water directly from rivers into which 
has flowed sewage from cities above them on the river. A few 
fortunate cities, such as Los Angeles and New York, bring their 
water supplies from protected areas far up in the mountains. In 
the case of cities where the water supply is polluted by sewage, 
filtration and chlorination are necessary. The water is passed 
through settling basins and sand filters which remove about 98 

Atnerican Museum of Natural History. 

Sand filter beds at Lawrence, Mass. 

per cent of the germs. Final treatment wdth hypochlorite of lime 
or liquid chlorine in very small amounts kills most of the remain- 
ing bacteria. In cities which drain their sewage into rivers and 
lakes, the problem of sewage disposal is large, and many cities 
now have means of disposing of their sewage in some manner 
which renders it harmless to their neighbors. 

Railroads may be responsible for carrying and spreading disease 
germs. It is said that a certain outbreak of typhoid in Scranton, 
Pa., was due to the fact that the excreta from a typhoid patient 
traveling in a sleeping car was washed by rain into a reservoir near 
which the train passed. Railroads, therefore, in one sense, are like 
great open sewers. 

Sewage Disposal. — Sewage disposal is an important sanitary 
problem for every city. Some cities, like New York, pour their 


sewage directly into rivers which flow into the ocean. Conse- 
quently, much of the liquid which bathes the shores of Manhattan 
Island is dilute sewage. Other cities, like Buffalo or Cleveland, 
send their sewage into the lakes from which they obtain their 
supply of drinking water. The city of Chicago has built a huge 
drainage canal which diverts water from Lake Michigan. Thus 
the sewage is diluted and carried eventually into the Mississippi 
River by way of the Illinois River. While there is not a noticeable 
increase in the bacterial content of the Illinois River at the point 
where it flows into the Mississippi, this drainage canal has done 
harm in another way. The fish in the upper Illinois River have 
been driven out or killed by the factory refuse and other wastes 
which come down the canal. This is only one example of the 
pollution of rivers by sewage and especially by factory wastes. All 
over the eastern part of our country rivers have been made open 
sewers, and now the conservation of our fish, as well as the water 
supply of many of our cities, is becoming a serious problem. 

.*^3^' 'M.;. 3i%*^ • 'i . ^^'^ *"'l^*i^-C' 



This chart shows that during a cholera epidemic in 1892 there were hundreds 
of cases of cholera in Hamburg, which used unfiltered water from the Elbe, but in 
adjoining Altona, where filtered water was used, the cases were very few. 

The best way to avoid the pollution of rivers is by proper 
sewage disposal, even if this method is expensive. Sewers for 
large cities are planned so that the dilute sewage is carried to a 
sewage disposal plant, usually situated a short distance outside 
of the community. Here the solid wastes are screened out, and 
then the smaller particles are precipitated out. The disposal of the 
soUd material, called sludge, becomes a serious problem. London 
and New York, each with millions of tons a year, dump their sludge 
out at sea, where it becomes a nuisance to the people living on the 


near-by shores. Chicago dumps sludge, untreated, into the 
drainage canal and the Illinois River. Sludge from small commu- 
nities can be buried or spread on some flat area to dry, but for large 
cities the best way to dispose of it seems to be by means of sludge 
tanks, where bacteria are allowed to work on it and decompose it. 

American Museum of Natural History. 
Protection against typhoid infection. 

The fluid sewage, after the solid matter is taken out, is usually 
run over filter beds composed of coarse sand, or over trickling 
filters composed of small stones. In these filters bacteria oxidize 
the remaining organic matter of the sewage, so that the hquid 
which flows off is harmless and odorless. StiU another method is 
to let the sewage flow over sandy land, later using this land for the 
cultivation of crops. This method is used by many smaU Euro- 
pean cities. It is possible for use only in rather small cities. 

The Work of the Department of Street Cleaning. — Another city 
problem is the disposal of refuse and garbage so that it will not be 
a menace to the health of the citizens. The city streets, when dirty, 
contain countless millions of germs which have come from decaying 
material, or from people and animals more or less diseased. In 
most large cities a department of street cleaning not only cares for 
the removal of dust from the streets, but also has the removal of 
garbage, ashes, and other waste as a part of its work. The disposal 



of solid wastes is a tremendous task. In Manhattan the dry 
wastes are estimated to be 1,000,000 tons a year in addition to about 
175,000 tons of garbage. Prior to 1895 in the city of New York 
garbage was not separated from ashes ; now the law requires that 
garbage be placed in separate receptacles from ashes. Do you 
see why? In some cities, such as Minneapolis, garbage must be 
wrapped in paper. This aids burning it in the city incinerator. 
The street-cleaning department should be aided by every citizen ; 
rules for the separation of garbage, papers, and ashes should be 
obeyed. Garbage and ash cans should be covered. Best results 
in street cleaning in summer are obtained by washing or flushing 
the streets, for thus the dirt containing germs is prevented from 
getting into the air. The garbage is removed in carts, and part 
of it is burned in huge furnaces. The animal and plant refuse 
may be cooked in great tanks, the fats extracted from this material, 
and the solid matter sold for fertilizer. Ashes are used in some 
places for filling marsh 
land. Thus the removal 
of waste matter may pay 
for itself in a large city. 

An Experiment in Civic 
Hygiene. — During the 
summer of 1913 an inter- 
esting experiment on the 
relation of flies and filth 
to disease was carried on 
in the city of New York 
by the Bureau of Public 
Health and Hygiene of 
the New York Associa- 
tion for Improving the 
Condition of the Poor. Two adjoining blocks were chosen in a 
thickly populated part of the Bronx near stables which were the 
breeding places of great numbers of flies. In one block all houses 
were screened, garbage pails were furnished with covers, refuse was 
removed, and the surroundings made as sanitary as possible. In 
the adjoining block conditions were left unchanged. During the 
summer as flies began to breed in the manure heaps near the stables, 

Dumping a load of ashes and rubbish into a scow, 
to be taken out to sea for final disposal. 


all manure was disinfected. Thus the breeding of flies was checked. 
The campaign of education was continued during the summer by- 
means of moving pictures, nurses, boy scouts, and school children 
who became interested. At the end of the summer it was found 
that there had been a considerable decrease in the number of cases 
of fly-carried diseases and a still greater decrease in the total days 
of sickness (especially of children) in the screened and sanitary 
block. If such a small experiment shows results like this, then 
what might a general clean-up of an entire city show? 

Public Hygiene. — Although it is absolutely necessary for each 
individual to obey the laws of health in order to keep well, it has 
become necessary also, especially in large cities, to have a depart- 
ment or board of health to exercise general supervision over the 
health of the people living in the community. In addition to such 
a body in cities, supervision over the health of citizens is also 
exercised by state boards of health. Since 1912 we have had super- 
vision over interstate quarantine and public health in general, 
exercised by the United States Public Health Service. Its valuable 
reports and reprints are available for schools and should be used 
in your project and class work. 

The Functions of a City Board of Health. — The administration 
of the board of health of a city includes a number of divisions, 
each one of which has a different work to do. Each is in itself 
important, and, working together, the entire machine provides 
ways and means for making a great city a safe and sanitary place in 
which to live. A local health board, according to the authority, 
Dr. C. E. A. Winslow, should supervise the food supplies and sani- 
tation of a city. It should from its laboratories take care of the 
communicable diseases, especially of tuberculosis. It should have 
a department of child hygiene and should carry on health cam- 
paigns through its department of publicity and education. Fi- 
nally, it should publish the vital statistics of the community. 

The Division of Communicable Diseases. — Communicable 
diseases are chiefly spread through personal contact. It is the duty 
of a government to prevent a person having such a disease from 
spreading it broadcast among his neighbors. This is done by the 
board of health, by the quarantine or the isolation of the person 
having the disease. No one save the doctor and the nurse should 


enter the room of the person quarantined. After the disease has 
run its course, the clothing, bedding, etc., in the sick room are dis- 
infected. This is known as terminal disinfection. 

The best cures for tuberculosis are rest, plenty of fresh out-of-door air, and 

wholesome food. 

How the Board of Health fights Tuberculosis. — Tuberculosis, 
which not many years ago killed fully one seventh of the people who 
died from disease in this country, now kills less than one tenth. 
This decrease has been brought about largely through the treat- 
ment of the disease. Since it has been proved that tuberculosis, 
if treated early enough, is cured by quiet living, good food, and 
plenty of fresh air and light, we find that numerous sanitariums 
have come into existence which are supported by private .or public 
means. At these sani- 
tariums the patients 
live out of doors, and 
sleep in the open air, 
and have plenty of 
nourishing food and 
little exercise. The 
Department of Health 
of the city of New 
York maintains a sani- 
tarium at Otisville in 
the Catskill Mountains 
and similar sanitariums are maintained by most large cities. There 
are many private sanitariums as well, maintained by various be- 
nevolent orders. Here people who are unable to provide means 
for getting away from the city are cared for, and a large per- 


A sanitarium for tuberculosis. 


cent age of them are cured. In this way and by laws which re- 
quire proper air shafts and window ventilation in tenement houses, 
by laws against spitting in public places, and in other ways, the 
boards of health in our towns and cities are waging war on tuber- 
Theodore Roosevelt said, in one of his messages to Congress : 

" There are about 3,000,000 people seriously ill in the United States, of 
whom 500,000 are consumptives. More than half of this illness is preventable. 
If we count the value of each life lost at only $1700 and reckon the average 
earning lost by illness at $700 a year for grown men, we find that the economic 
gain from mitigation of preventable disease in the United States would exceed 
$1,500,000,000 a year. This gain can be had through medical investigation 
and practice, school and factory hygiene, restriction of labor by women and 
children, the education of the people in both publid and private hygiene, and 
through improving the efficiency of our health service, municipal, state, and 

Work of the Division of School and Infant Hygiene. — Besides 
the division of communicable diseases, the division of sanitation, 
which regulates the general sanitary conditions of houses and their 
surroundings, and the division of inspection, which looks after the 
purity and conditions of sale and delivery of milk and foods, there 
is another division which most vitally concerns school children. 
This is the division of school and infant hygiene, which supervises 
the care of the children of the city. 

Adenoids. — Many children suffer needlessly from enlarged 
tonsils and ad'enoids, — growths in the back of the nose or mouth 
which prevent admission of sufficient air to the lungs. A child 
suffering from these growths is usually a ^^ mouth breather." The 
result to the child may be deafness, chronic running of the nose, 
nervousness, and lack of power to think. His body cells are 
starving for oxygen. A very simple operation removes this 
growth. Cooperation on the part of the children and parents with 
the doctors or nurses of the board of health will do much in removing 
this handicap from many young lives. 

Eyestrain. — Another handicap to a boy or a girl is eyestrain. 
Twenty-two per cent of the school children of Massachusetts 
were recently found to have defects in vision. Tests for defective 
eyesight may be made at school easily by competent doctors, and 


if the weakness is corrected by procuring proper glasses, a handicap 
on future success will be removed. 

Decayed Teeth. — Decayed teeth are another handicap, cared 
for by this division. Free dental clinics have been established in 
many cities, and if children will do their share in caring for their 
teeth, the chances of their success in later life will be greatly aided. 
Boys and girls, if handicapped with poor eyes or teeth, do not 
have a fair chance in life's competition. In a certain school in 
New York there were 236 pupils marked '' C " in their school 
work. These children were examined, and 126 were found to 
have bad teeth, 54 to have defective vision, and 56 to have 
other defects, as poor hearing, adenoids, enlarged tonsils, etc. 
Of these children 185 were treated for these various difficulties, 
and 51 did not take treatment. During the following year's 
work 176 of these pupils improved from '^ C " to '' B " or '' A," 
while 60 did not improve. If defects are such a handicap in 
school, what would be their effect on the chances of success in life 

In conclusion : this department of school hygiene deserves the 
earnest cooperation of every young citizen, girl or boy. If each of 
us would honestly help by maintaining quarantine in the case of 
communicable disease, by observing the rules of the health depart- 
ment, by acting upon reliable advice in case of eyestrain, bad teeth, 
or adenoids, and most of all by observing the rules of personal 
hygiene, the community in which we live would, a generation 
hence, contain stronger, more prosperous, and more efficient 

Summary. — This chapter has first tried to show how we may 
improve living conditions in our own homes through the application 
of some simple laws of hygiene and sanitation. 

Second, it has shown how a little unselfishness and cooperation 
will help to make our community a better place in which to live. 

Third, it has shown how state and city departments of health 
and other agencies are at work to safeguard our milk and water 
supplies, to protect us through proper disposal of sewage, to care 
for our city health by ash and garbage collection. 

Fourth, it has shown how some of the agencies which guard 
our community health do their work. 


Problem Questions 

1. Discuss the various ways in which you can make your home a more 
healthful place. (This would make a good project, report.) 

2. Discuss some ways in which we can control bacteria in our homes. 

3. Discuss ways and means of making our school a healthier and pleasanter 
place in which to work and play. 

4. What are some means for the protection of industrial workers? (Look 
up government pubhcations and make this a project report.) 

5. How is your milk supply safeguarded? Are the standards given on 
page 302 conformed with in your community? 

6. Make a report on your local water supply and check up with what you 
have learned. Is your supply adequately protected? 

7. Discuss sewage disposal in relation to your community. Is there pollu- 
tion of streams there? 

8. How does your community care for its streets? Do you have adequate 
protection ? 

9. Does your board of health function properly? What duties does it 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Allen, Civics and Health. Ginn and Company. 

Broadhiu-st, Home and Community Hygiene. J. B. Lippincott Company. 

GuUck Hygiene Series, Town and City. Ginn and Company. 

Hough and Sedgwick, The Human Mechanism, Part II. Ginn and Company. 

Hutchinson, Preventable Diseases. Houghton MiflElin Company. 

Marshall, Microbiology. P. Blakiston's Son and Company. 

Morse, The Collection and Disposal of Municipal Waste. Municipal Journal 

and Engineer. 
Richards, Sanitation in Daily Life. Whitcomb and Barrows. 
Richmond and Wallach, Good Citizenship. American Book Company. 
Ritchie, Primer of Sanitation. World Book Company. 
Tolman, Hygiene for the Worker. American Book Company. 
Winslow, Healthy Living. Charles E. Merrill Company. 

REPORTS, etc. 

Hygeia. American Medical Association. 

Reports of Boards of Health of California, Illinois, New York, Virginia, etc.; 

and of the City of New York and other cities. 
Bulletins and Publications of Committee of One Hundred on National Health. 
School Hygiene, American School Hygiene Association. 
Public Health Reprints: 54, 78, 106, 192, 234, 302, 341, 441, 448, 499, 530; 

680, 723, 821, 827, 850. 
Farmers' Bulletins: 70, 658, 851, 1227. 




Problem : Man's relation to forests. 

(a) What is the value of forests to man f 

(h) What can man do to prevent forest destruction f 

Laboratory Suggestions 

Field exercise. Study of cross sections of tree trunks to determine struc- 
ture and approximate age. 

Demonstration of some uses of wood. Optional exercise on structure of wood. 
Home work on study of furniture trim, etc. 

Laboratory study or visit to museum to study some economic uses of wood. 

Visit to museum or field trip to learn to recognize some common trees. 

Project. To make a tree survey of my town. 

Project. To make a survey of the forest resources in my locality. 

The Economic Value of Trees. Protection and Regulation of 
Water Supply. — No one who has traveled over the great South- 
west can fail to see the value of forest trees. Great areas of land 
lie devastated, subject to floods in winter and droughts in summer. 
Yet these areas, if given water supply, would be capable of pro- 
ducing crops in abundance. Irrigation has proved this in regard 
to similar areas. Irrigation projects, which now give homes and 
employment to thousands of people, besides producing annually 
great quantities of food supplies, would be impossible were it not 
for protected forest areas. Moreover, nearly 800 western com- 
munities, with a population of nearly 3,000,000, depend for their 
water supplies upon streams coming from areas protected by 
national forests. When the earth's surface is covered by trees they 
prevent soil from being washed away and they hold moisture in the 




ground. Devastation of immense areas in China and considerable 
damage by floods in parts of Switzerland, France, and the United 
States have resulted where the forest covering has been removed. 
The annual spring " freshets " in the Ohio and Mississippi valleys, 
with all too frequent loss of both life and property, are due to the 
lack of forest protection at the sources of these rivers. It has been 
estimated that the carrying power of water is increased 64 times 

if its rate of flow is 
doubled; that is, the 
transporting power of 
water varies as the sixth 
power of its velocity. 
This accounts for the 
tremendous destruction 
produced by a mountain 
stream in flood. 

Prevention of Erosion 
by Covering of Organic 
Soil. — It is hard to 
realize the vast amount 
of soil that is dug out 
by ungoverned streams 
and carried far from its 
original source. Exam- 
ples of what streams 
have done may be seen in the great canyon of the Colorado River 
and the filling up of the Gulf of California with debris, or in 
the huge deltas of the Nile and of the Mississippi River. The 
forests prevent erosion in other places by holding back the water 
supply and letting it out gradually. This they do by covering 
the inorganic soil with humus or decayed organic material which, 
like a sponge, holds water through long periods of drought. It is 
estimated that the forest floor can absorb and hold for some time 
a rainfall of between four and five inches. Thus it regulates the 
flow off. The roots of the trees, too, help hold the soil in place 
and prevent erosion. The gradual evaporation of water through 
the stomata of the leaves cools the atmosphere, and this tends to 
precipitate the moisture in the air. Eventually the dead bodies 

Result of deforestation in China. This land 
has been ruined by erosion. (Carnegie Institu- 
tion Research in China.) 


of the trees themselves are added to the organic covering, and 
new trees take their place. 

The Forest Regions of the United States. — The total forest 
area of the United States to-day is less than 470,000,000 acres. 
More than 80,000,000 acres have been burned or cut, so that to-day 
they are waste land. We have more waste forest land than the 
combined forest areas of western Europe. Our present forests are 
rapidly decreasing, due to the demands of an increasing population, 
a woeful neglect on the part of the owners of the land, and waste- 
fulness on the part of cutters and users alike. 

The different kinds of forest in the United States. 

A glance at the above map shows the distribution of our forests ; 
but it must be remembered that most of the land fit for farming 
has been cleared. Washington ranks first in the production of 
lumber. Here the great Douglas fir, one of the '' evergreens " 
or coniferous trees, forms the chief source of supply. In the South- 
ern states, especially Louisiana and Mississippi, yellow pine and 
cj^ress are the trees most lumbered. In what other Southern 
states are there coniferous forests ? In what Northern states are 
such forests found? The supply of hardwoods comes from the 
deciduous and mixed forests. 


Values of the Forest. — We have learned that forests regulate 
the water supply. Much organic soil is formed from rotted trees 
and other vegetation. In some localities forests are used as 
windbreaks and to protect mountain towns against avalanches. 
In winter they moderate the cold, in summer they reduce the heat 
and lessen the danger from storms. Birds nesting in the woods 
eat insects and thus protect many valuable plants. The forest 
gives a refuge for wild animals, particularly game such as deer, 
elk, and antelope. There are now nearly 12,000,000 acres set 
aside as refuges for wild birds and game, that they may not become 
extinct as have a few native wild animals. The clear streams of 
the forest are the homes of many of our best game fishes. And 
perhaps best of all, the forest has become the playground for lovers 
of the out-of-doors in our nation. 

In addition our forests have an enormous economic value. 
Useful in so many ways, they are one of our great sources of 
national wealth. 

Uses of Wood. — Even in this coal-burning age, wood is still 
the most used fuel. Few buildings have been made that do not 
use wood in their construction. Wood outlasts iron under water, 
in addition to being light. It is cheap and, with proper care of the 
forests, inexhaustible, while our mineral wealth may some day be 
used up. Distilled wood gives wood alcohol. Partly burned 
wood is charcoal. In our forests much of the soft wood (the conif- 
erous trees, spruce, balsam, hemlock, and pine), and poplars, 
aspens, basswood, with some other species, make paper pulp. The 
daily newspapers and cheap books are responsible for inroads on 
our forests which cannot well be repaired. It is not necessary to 
take the largest trees to make pulp wood, hence many young trees 
of not more than six inches in diameter are sacrificed. Of the 
hundreds of species of trees in our forests, the conifers are prob- 
ably most sought after for lumber. Pine, especially, is probably 
used more extensively than any other wood. It is used for all 
heavy construction work, frames of houses, bridges, masts, spars 
and timber, of ships, floors, railway ties, and many other purposes. 
Cedar is used for shingles, cabinet work, lead pencils, etc. ; hem- 
lock and spruce for heavy timbers. Another use for our lumber, 
especially odds and ends of all kinds, is in the packing-box industry. 



Hemlock bark is used for tanning. Wood is used for making 
artificial silk, manufactured from the fiber of aspen, basswood, 
Cottonwood, and other trees. The hard woods, ash, red gum, 
beech, birch, cherry, chestnut, elm, maple, oak, and walnut, are 
used largely for the " trim " of our houses, for manufacture of 
furniture, wagon or car work, and for endless other purposes. 
Our hardwood supply is rapidly becoming exhausted, particularly 

Photo by W. I. Hutchinson , Courtesy U. S. Forest Service. 
Logging with a tractor, Lassen National Forest, California. 

ash and hickory, and our only remedy is to plant more trees of 
this kind. 

Forest Waste. — Our forests are being cut off at the rate of 
about 10,000,000 acres a year. But man loses much of this wood 
by wasteful methods of lumbering. Hundreds of thousands of 
dollars' worth of lumber is left to rot annually because the lum- 
bermen do not cut the trees close enough to the ground, or because 
through careless felling of trees many other smaller trees are 
injured. This is particularly true among the large trees in our 
western forests. There has been great waste also in the lumber 
mills. In fact, man wastes lumber in every step from the forest to 
the finished product. 

Fire an Enemy. — Indirectly, man is responsible for fire, one of 
the greatest enemies of the forest. Most of the great forest fires 
of recent years, the losses from which total in the hundreds of 



millions, have been due to smokers, to railroads, or to carelessness 
in making camp fires in the woods. It is estimated that fires have 
destroyed nearly 12,000,000 acres of forest and caused a money 
damage of over $17,000,000 a year. In the past great forest fires 
have devastated Minnesota, Wisconsin, and Michigan with a loss 
of thousands of lives and hundreds of millions of dollars. In 
addition to the loss in timber, the fires often burn out the organic 
matter in the soil (the '^ duff ") forming the forest floor, thus 
preventing the growth of new forests for many years to come. 

Effect of forest fire. 

The United States Forest Service and the state forestry depart- 
ments are constantly on guard against forest fires. Fire lookouts 
are established at places most favorable for observation of large 
areas. If a fire starts, notice is sent at once to the forest rangers 
in that locality so that the fire may be put out before it spreads. 
State and Federal governments alike do their best to protect our 
forests. We must do our share in this work by taking care with 
camp fires or bonfires when we are in the woods. 

Other Enemies. — Other enemies of the forest are numerous 
fungus plants, insect parasites which bore into the wood or destroy 
the leaves, and grazing animals. The chestnut blight is an 
example of a fungus parasite which it has seemed impossible to 
combat. It has killed most of the chestnut trees in the eastern 
states and has gone as far south as the Carolinas. Our only hope 
for the chestnut appears to be in finding some chestnuts that are 


immune to the disease. The Englemann spruce beetle has 
destroyed millions of feet of lumber in the Rocky Mountains, and 
the Black Hills beetle has done great damage in South Dakota. 
Hundreds of other insect enemies, some of them imported, are 
doing very great damage, especially in our Eastern states. The 
gypsy and brown-tail moths are examples of such pests. Live 
stock, especially sheep, may do much harm in a forest by eating 
young shoots and trampling on young trees. Storm, wind, and 
lightning do damage also, as trees which have been uprooted soon 
die and thus make an excellent place for fire to start. 

Forestry. — In some parts of central Europe, the value of the 
forests was seen as early as 1300 a.d., and many towns consequently 
bought up the surrounding forests. The city of Zurich has owned 
forests in its vicinity for at least 600 years and has found them a 
profitable investment. Europe has long led the way in showing 
how to care for forests and how to make them pay. In this 
country only recently has the importance of preserving and caring 
for our forests been noted by our government. Now, however, 
we have a Forest Service in the Department of Agriculture and 
this and numerous state and university Schools of Forestry are 
teaching the people of this country the best methods for the pres- 
ervation of our forests. The Federal government has set aside a 
number of tracts of mountain forest, principally in the Western 
states and Alaska, which are under the control of the National 
Forest Service, Department of Agriculture. In 1924 these had 
an area of more than 157,500,000 acres, an area greater than New 
England and New York, New Jersey, Delaware, Pennsylvania, 
Maryland, Virginia, and West Virginia. New York has established 
for the same purposes the Adirondack and Catskill Mountain Forest 
Preserves, with nearly 2,000,000 acres of timber land ; Pennsyl- 
vania has preserves of more than 1,250,000 acres, and many other 
states have followed their example. Wisconsin, Minnesota, and 
Michigan each have more than 200,000 acres set aside, and the 
total area for all the states is about 4,300,000 acres. 

Methods for Keeping and Protecting the Forests. — Forests 
should be kept thinned. Too many trees are almost as bad as 
too few. They struggle with one another for foothold and light, 
which only a few can enjoy. The cutting of a forest should be 



considered as a harvest. The oldest trees are the '' ripe grain," 
and the younger trees are to be left to grow to maturity. Several 
methods of renewing the forest are in use in this country. (1) Trees 
maybe cut down and young ones allowed to sprout from cut stumps. 
Beech, chestnut, and the redwood of California are among the 
trees that grow in this w^ay. This is called coppice growth. 
(2) Areas or strips may be cut out so that seeds from neighboring 
trees are carried there by the wind to start new growth. (3) Forests 
may be artificially planted. Two seedlings planted for every tree 

The forest primeval. Trees kill 
each other in a constant struggle for 
light and air. 

Beech forest in Germany. The trees 
are kept thinned out to allow the young 
trees to get a start. 

cut is a rule followed in Europe. (4) The most economical method 
is that shown in the second picture on this page, where the largest 
trees are thinned out over a large area so as to make room for the 
younger ones to grow up. Our forest service is trying to interest 
farmers in planting trees for profit, and many thousands of trees are 
set out each year. But in 1925 it was estimated that we were 
using up our forest about four times as fast as it was growing, 
so that we need much more planting if we are to keep our forests 
at approximately their present area. 

A City's Need of Trees. — The city of Paris, well known as one 
of the most beautiful of European capitals, spends over $100,000 
annually in caring for and replacing some of its 90,000 trees. AW 


over the United States municipal governments are beginning to 
realize what European cities have long known, that trees are of 
great value to a city. They are planting trees and protecting them. 
Many cities have appointed city foresters, who care for the trees 
in the parks and along the streets. Many municipalities plant 
trees and tax the property owners who receive benefit thereby, for 
trees and shrubs have an ornamental value that is expressed in 
dollars and cents. Perhaps the most hopeful sign is that people 
everjrwhere are beginning to realize the value of our trees and the 
need for their protection and conservation. Arbor Day is set 
aside for tree planting and to teach young people some of the 
reasons why trees are of value to mankind. Let us all try to make 
Arbor Day what it should be, a day for caring for and planting 
trees ; thus we may assist to preserve this most important heritage 
of our nation. 

Summary. — Trees regulate water supplies by holding water 
in the soil where they are growing. Wherever man has deforested, 
there come floods and erosion, with a loss of organic soil. In addi- 
tion, forests are refuges for birds and other animals and make 
wonderful outdoor playgrounds. Wood, both for fuel and for 
lumber and for other forest products, must be conserved by regulated 
cutting and reforestation. Waste in the forest and at the mill 
must be stopped or we shall lose this most precious of our national 
resources. Losses by fire, as well as those caused by insect enemies, 
are very great. Our one hope lies in educating people to realize 
the value of forests. Forestry as a profession should be chosen by 
more boys and all of us should do our share to protect this great 
asset, the forest. 

Problem Questions 

1. What effect do forests have on water supplies? On soil making? On 
erosion? Can you determine the effect that forests have on your own com- 
munity ? 

2. Of what direct economic values are the forests? 

3. List the various uses of wood in your community. 

4. What is the cause of the greatest loss in forests ? To what extent does 
smoking cause forest fires? How might we avoid this loss? 

5. How may parasitic enemies harm the forest ? How can we control some 
of these pests? 


6. Show several ways in which our forests may be saved and increased by 
scientific methods of forestry. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Emerson and Weed, Our Native Trees. J. B. Lippincott and Company. 

Matthews, Familiar Trees and Their Leaves. D. Appleton and Company. 

JMayne and Hatch, High School Agriculture. American Book Company. 

Pack, The School Book of Forestry. The American Tree Association. 

Pinchot, A Primer of Forestry, Division of Forestry, United States Depart- 
ment of Agriculture. 

Pinchot, The Training of a Forester. J. B. liippincott and Company. 

Coulter, Barnes, and Cowles. A Textbook of Botany, Part I and Vol. II. Ameri- 
can Book Company. 

Farmers' Bulletins: 265, 963, 1208, 1209, 1241, 1417. 

Annual Reports of the Forest Service. 


Problems : To find out how green plants are useful to man : 

(a) As food. 

(h) In supplying material for clothing. 

(c) In other ways. 

To find out how green plants are harmful to man. 

Suggested Laboratory Work 

If a commercial museum is available, a trip should be planned to supple- 
ment the work in this chapter. The school collection may include most of 
the examples mentioned, both of useful and of harmful plants. 

A study of weeds and poisonous plants should be taken up in actual labora- 
tory work, either by collection and identification or by demonstration. 

Home Project. A weed survey of my home yard or my neighborhood. 

Green Plants have a " Dollar and Cents " Value. — To the girl 
or the boy living in the city green plants seem to have little direct 
value. Although we see vegetables for sale in stores and we know 
that fruits have a money value, we are apt to forget that the wealth 
of our nation depends upon crops more than it does on manufac- 
tories and business houses. The economic or " dollars and cents " 
value of plants is enormous ; and our lives depend on the food 
which they supply. 

We have already seen some of the uses to mankind of the prod- 
ucts of the forest ; let us now consider some other plant products. 

Leaves as Food. — Grazing animals feed almost entirely on 
tender shoots or leaves, blades of grass, and other herbage. We 
realize the economic value of grass when we remember that for a 
period of ten recent years the average hay crop in this country was 
worth well over $1,000,000,000 a year. And this does not count 
the wild grasses used for fodder by countless grazing animals. 

Certain leaves and buds are used as food by man. Lettuce, 



Cabbage Onions 

Leaves used as food. 


beet tops, kale, spinach, broccoli, are examples. A cabbage 

head is nothing but a big bud which has been cultivated by man. 

An onion is a compact budlike mass of thickened leaves which 

contain stored food. 

Stems as Food. — A city child, if asked to name some stem used 

as food, probably would mention either asparagus or celery. We 

sometimes forget that one 
of our greatest necessities 
comes largely from the 
stem of the sugar cane. 
An average of over 100 
pounds of sugar is used 
each year by each person 
in the United States. To 
supply the growing de- 
mand for sugar, beets 
are now being raised in 
many parts of the world, 
so that nearly half the 
total supply of sugar comes 
from this source. In this 
country we produce al- 
most six times as much 

sugar from beets as from cane. Maple sugar is a well-known 

commodity which is obtained by boiling the sap of sugar maples 

Celery Kohl-rabi Potato 
Stems used as food. 

Sugar cane 



until it crystallizes when cold. More than 16,000 tons of maple 
sugar is obtained every spring, Vermont producing about 40 per cent 
of the total output. The sago palm is another stem which supports 
the life of many natives in Africa. Another stem, growing under- 
ground, forms one of man's staple articles of diet ; this is the potato. 

Roots as Food. — Roots which store food for plants form an 
important part of man's vegetable diet. Beets, radishes, carrots, 
parsnips, sweet potatoes, and many others might be mentioned. 

The following table shows the proportion of nutrients in some of 
the more common roots and stems : 

Potato . . 

Carrot . . 

Parsnip . . 

Turnip . . 

Onion , . 
Sweet potato 

Beet . . . 





















Fruits and Seeds as Foods. — Our cereal crops, corn, wheat, 
etc., have played a very important part in the civilization of man 

Wheat Nuts Pear 

Seeds and fruits used for food. 


and are now of so much importance to him as food products that 
bread made from wheat flour has been called the " staff of life." 
Our grains are the cultivated progeny of wild grasses. Domesti- 



cation of plants and animals marks epochs in the advance of civili- 
zation. The man of the stone age hunted wild beasts for food, 
and lived like one of them in a cave or wherever he happened to 
be ; he was a nomad, a wanderer, with no fixed home. He may 
have discovered that wild roots or grains were good to eat; per- 
haps he stored some away for future use. Then came the idea of 
growing things at home instead of digging or gathering the wild 
fruits from the forest and plain. The tribes which first cultivated 
the soil made a great step in advance, for they had as a result a 
fixed place for habitation. The cultivation of grains and cereals 
gave them a store of food which could be used at times when other 
food was scarce. The word " cereal " (derived from Ceres, the 
Roman goddess of agriculture) shows the importance of this crop 
to Roman civilization. From earliest times the growing of grain 
and the progress of civilization have gone hand in hand. As 
nations have advanced in power, their dependence upon the cereal 
crops has been greater and greater. 

" iDdian corn," says John Fiske, in The Discovery of America, " has played 
a most important part in the history of the New World. It could be planted 
without clearing or plowing the soil. There was no need of threshing or win- 
nowing. Sown in tilled land, it yields more than twice as much food per acre 
as any other kind of grain. This was of incalculable advantage to the English 
settlers in New England, who would have found it much harder to gain a se- 
cure foothold upon the soil if they had had to begin by preparing it for wheat 
or rye." 

To-day, in spite of the great wealth which comes from our 
mineral resources, live stock, and manufactured products, the 
surest index of our country's prosperity is the size of the corn 
and wheat crop. According to a recent report, the value of farm 
property in the United States is more than $78,000,000,000, a much 
greater amount than is invested in manufacture. 

Corn. — More than 3,000,000,000 bushels of corn were raised in 
the United States during the year 1923. This -figure is so enor- 
mous that it has but little meaning to us. Iowa and Illinois are 
the greatest corn-producing states in this country, each having a 
yearly record of over 400,000,000 bushels. The figure on page 327 
shows the principal corn-producing areas in the United States. 

Indian corn is put to many uses. It is a valuable food. It 



has a large proportion of starch, from which glucose (grape sugar) 
and alcohol are made. Machine oil and soap are made from it. 
The leaves and stalks are excellent fodder; they can be made 
into paper and packing material. Mattresses can be stuffed with 
the husks. The pith is used as a protective belt placed below the 
water line of our huge battleships. Corn cobs are used for fuel, 
one hundred bushels having the fuel value of a ton of coal. 

Corn-producing regions in the United States. Each dot = 300,000 bushels. 

Wheat. — Wheat is the crop of next greatest importance in 
this country. Nearly 900,000,000 bushels were raised in this 
country in 1923, representing a total money value of over 
$725,000,000, although during the World War our farmers received 
nearly $2,000,000,000 yearly for a crop of less than 1,000,000,000 
bushels. Seventy-two per cent of all the wheat raised comes from 
the North Central states and the far West. Much of the wheat 
crop is exported, thus indirectly giving employment to thousand-j 
of people on railways and steamships. Wheat is used chiefly for 
manufacture into flour. The germ, or young wheat plant, is sifted 
out during this process and made into breakfast foods. Flour 
making forms the chief industry of Minneapolis, Minnesota, and 
of several other large and wealthy cities in this country. 


Other Grains. — Of the other cereals raised in this country, oats 
are the most important crop, more than 1,500,000,000 bushels hav- 
ing been produced in 1923. Barley and rye, grains much like 
wheat, are produced in smaller quantity. One of the most impor- 
tant grain crops for the world is rice. The fruit of this grasslike 
plant, after threshing, screening, and milling, forms the principal 
food of one third of the human race. 

Wheat-producing regions in the United States. Each dot = 200,000 bushels. 

Garden Fruits and Vegetables. — Vegetables have come to play 
an important part in the dietary of man. People in this country 
are beginning to find that more vegetables and less meat are better 
than the meat diet so often used. Market gardening forms the 
lucrative business of many thousands of people near our great cities 
and of still more in our Southern states. Some of the important 
fruits are squash, cucumbers, pumpkins, melons, tomatoes, peppers, 
strawberries, raspberries, and blackberries. As many as 500 car- 
loads of melons were shipped from the Imperial Valley, California, 
during a single day in 1925. More than $150,000,000 worth of 
fruits are canned or dried each year in addition to what is sold fresh. 
Beans and peas are important as foods because of their relatively 



large amount of protein. Canning green corn, peas, beans, and 
tomatoes has become an important industry. 

Orchard and Other Fruits. — In the United States about 
200,000,000 bushels of apples are grown every year. Pears, plums, 
apricots, peaches, and nectarines also are raised in large orchards, 
especially in California and in Georgia. Nuts form one of our 
important articles of food, largely because of the great amount of 
protein contained in them. 
Walnut ranches are now 
very profitable, especially 
in California. 

The grape crop of the 
world is commercially valu- 
able, because of the raisins 
produced. The culture of 
lemons, oranges, and grape- 
fruit has increased in recent 
years in this country as 
well as in other parts of 
the world. Figs, olives, and 
dates also are grown now 
in the Southwest ; they are 
staple foods in the Mediter- 
ranean countries and are 
sources of wealth to the 
people there, as are coco- 
nuts, bananas, and many 
other fruits in tropical coun- 

Beverages and Condiments. — The coffee and cacao beans, the 
leaves of the tea plant, products of tropical regions, form the basis 
of very important beverages of civilized man. Black and red 
pepper, mustard, allspice, nutmegs, cloves, and vanilla are all 
products from various fruits and seeds of tropical plants. 

Raw Materials. — • Green plants have many other uses, besides 
supplying food. Many of our city industries would not be in 
existence were it not for certain plant products which furnish the 
raw materials. Many cities of the East and South, for example, 

Picking apples, an important crop in some 
parts of the United States. 


depend upon cotton to give employment to thousands of factory- 

Cotton. — Of our native plant products cotton is probably of 
the most importance to the outside world. More than ten million 
bales of five hundred pounds each are raised annually, although 
the cotton boll weevil has greatly reduced the crop in some regions. 

Cotton-producing regions in the United States. Each dot = 4000 bales. 

The cotton plant thrives in warm regions. Its commercial 
importance is gained because the seeds of the fruit have long fila- 
ments attached to them. Bunches of these filaments, after treat- 
ment or ginning, are easily twisted into threads from which are 
manufactured cotton cloth, muslin, calico, and cambric. In ad- 
dition to the fiber, cottonseed oil, a substitute for olive oil, is 
made from the seeds, and the refuse makes fodder for cattle. 

Vegetable Fibers. — Among the important vegetable fibers 
besides cotton are Manila hemp, which comes from the leaf-stalks 
of a plant of the banana family, and true hemp, which is the bast 
or woody fiber of a plant cultivated in most warm parts of the 
earth. Flax is another important fiber plant, grown largely in 
Russia, Ireland, and other parts of Europe. Flax is becoming a 
more important crop in this country since the shortage caused 



by the World War. Linen cloth is made from the bast fibers 
of the stem of this herb. Burlap and coarse bags are made from 
the fiber of the jute plant, raised in India. 

Vegetable Oils. — Some of the same plants which give fiber 
also produce oil. Cottonseed oil pressed from cotton seeds, lin- 
seed oil from the seeds of the flax plant, and coconut oil (the 
covering of the nut produces the fiber) are examples. One of the 
important industries of California is olive culture, the fruit being 
used as a table delicacy, while oil pressed from the fruit is a well- 
known table oil. 

Drug-producing Plants. — Quinine, the specific for malaria (page 
279), was known by the Indians in South America before the white 
men came. It is made from the bark of the cinchona tree. South 
America also furnishes us with co'caine, a habit-forming drug made 
from the leaves of the coca tree of Peru. Morphine and opium 
come from the poppy. Many of our pleasant oils and flavors as 
eucalyptus, wintergreen, peppermint, etc., come from plants. 

Harmful Green Plants. — We have seen that many green plants 
are very useful to man. There are, however, some that are harm- 
ful. For example, the poison ivy is extremely poisonous to touch. 


'm0m,^ .*^i- J 



Virginia creeper. 

Poison ivy. 

It is a climbing plant which attaches itself to trees or walls by 
means of tiny air roots which grow out from the stem. It has 
leaves divided in three parts, which aid in distinguishing it from its 
harmless climbing neighbor, the Virginia creeper, which has leaves 


divided in jive parts. Every boy and girl should know how poison 
ivy looks in order to avoid it. Injury from poison ivy may often 
be prevented by a prompt washing with soap and water. 

Tobacco, although strictly a poisonous plant because of the 
nicotine it contains, is, nevertheless, one of this country's largest 
crops. Nearly 1,500,000,000 pounds were raised in 1924, having 
a value of about $300,000,000. Atropine and belladonna, both 
deadly poisons used as drugs, are obtained from plants related 
to the tobacco. 

Numerous other poisonous common plants are found, one of 
which deserves special notice because of its presence in vacant 
city lots. The Jimson weed {Datura) is a bushy plant, from two 
to five feet high, bearing large leaves. It has white or purplish 
flowers, and later bears a four-valved seed pod containing several 
hundred seeds. These plants contain a powerful poison, and 
people are sometimes made seriously ill by eating the roots or other 
parts by mistake. 

Weeds and their Control. — From the economic standpoint 
the green plants which do the greatest damage are weeds. Those 
plants which provide best for their young are usually the most 
successful in life's race. Plants which combine with the ability 
to scatter many seeds over a wide territory the additional char- 
acteristics of rapid growth, resistance to extreme cold or heat and 
to attacks of enemies, inedibility, and peculiar adaptations to 
cross-poUination or to self-pollination, are usually spoken of as 
weeds. They flourish in the sterile soil of the roadside and in 
the fertile soil of the garden. By means of rapid growth they 
kiU other plants of slower growth by usurping their territory. 
Slow-growing plants are thus actually exterminated. Besides 
depriving other plants of soil salts and water, weeds do more 
harm. Some are poisonous, as the loco-weed, hemlock, and laurels. 
Cattle eating them may become poisoned. Other weeds, as the 
wild onion or garlic, may be eaten by cows, and the milk produced 
will be ruined in flavor. Some weeds are hosts to injurious para- 
sitic insects or fungi ; witness the Hessian fly, which lives in some 
wild grasses, and the wheat rust, which lives in the barberiy. The 
pollen of the ragweed and of other weeds undoubtedly causes some 
people to have '' hay fever." Many of our common weeds have 




been introduced from other countries and have, through their 
numerous adaptations, driven out plants which stood in their way. 
Such is the Russian thistle. A single plant of this kind will give 
rise to over 20,000 seeds. First introduced from Russia with 
imported flaxseed in 1874, by 1898 it had appeared as a pest in all 
states east of the Rocky Mountains. 

Weeds are introduced into lawns and fields often because their 
seeds are mixed with the good seeds which are sown there. Farm- 
ers should be sure of the quality of seed before planting it. Har- 
rowing and cultivating land helps to destroy weeds. We should 
use every method possible to prevent the weeds from producing 
seeds, because they are so numerous. Poisons are used in some 
cases ; sheep, which seem to prefer some weeds to grass, are also 
a great aid in keeping down these pests. 

Summary. — This chapter has explained the very great impor- 
tance of green plants in food production for man and the lower 
animals. Man is provided also with shelter, material for clothing, 
drugs, and many other commodities by the green plants. Some 
green plants do harm, as is proved by the presence of weeds and 
poisonous plants. 

Problem Questions 

1. Tabulate the useful plants of your locality. The harmful plants. 

2. How does the value of the present wheat or corn crop compare with the 
cost of building Panama Canal or a college ? 

3. What plants are used economically in your locality? Are there any 
useful plants not made use of there? 

4. What are weeds? How would you go to work to control them? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Atwood, Civic and Economic Biology. P. Blakiston's Son and Company. 

Whitbeck, Industrial Geography. American Book Company. 

Sargent, Plants and Their Uses. Henry Holt and Company. 

Toothaker, Commercial Raw Materials. Ginn and Company. 

Transeau, General Botany. World Book Company. 

United States Dept. of Agriculture, Farmers' Bulletins 17, 86, and others 



Problems : How molds and other fungi harm man. 
What yeasts do for mankind. 

A study of bacteria with reference to the good and the harm they 

Laboratory Suggestions 

Field work. Bracket fungi and chestnut blight. 
Home experiment. Conditions favorable to the growth of mold. 
Laboratory demonstration. Growth of mold, structure, drawing. 
Home experiment or laboratory demonstration. Conditions unfavorable for 
the growth of molds. 

Demonstration. Process of fermentation. 

Microscopic demonstration. Growing yeast cells. 

Home experiment. Conditions favorable for the growth of yeast. 

Demonstration. Tubercles containing nitrogen-fixing bacteria. 

Laboratory experiment. The value of preservatives. 

Saprophytic Fungi. — We have found that, on the whole, green 
plants are useful to manldnd. But not all plants are green. We 
have already seen the tremendous part that disease-producing 
bacteria play in our lives ; and most of us are familiar with some 
fungi, as the edible mushrooms and the so-called '' toadstools" 
found in parks or lawns. These plants contain no chlorophyll. 
They are as much dependent upon the green plants for food 
as are animals. But the bacteria and the fungi require for the 
most part dead organic matter for their food. This may be ob- 
tained from decayed vegetable or animal material in soil, from 
the bodies of dead plants and animals, or even from foods pre- 
pared for man. Fungi which feed upon dead organic material 
are known as sap'rophytes. Examples are the mushrooms, yeasts, 
and molds. 




Some Parasitic Fungi. — Other fungi prefer living plants or 
animals for their food and are therefore classed as parasites. An 
example is the chestnut blight, which has killed chestnut trees 
by the thousands in the eastern 
part of the United States. It 
produces millions of tiny spores ; 
which, blown about by the 
wind, light on the trees, sprout, 
and send under the bark thread- 
like mycelia which absorb the 
food circulating in the living 
cells, eventually causing the 
death of the tree. 

Another fungus which does 
much harm to trees is the shelf 
or bracket fungus. The shelf - 
like body is in reality the re- 
productive part of the plant ; 
in its lower surface are formed 
millions of asexual spores, 
which, when they fall on a dead 
or a dying tree trunk, may start 
a new fungus growth. The true body of the plant, a network 
of threads, is found under the bark. Once established, it spreads 
rapidly. There is no remedy except to kill the tree and burn it, 

United Stales Dept. of Agric. 

Tree being killed by chestnut canker. 

Shelf fungus, or bracket fungus, on a small branch. 

so as to destroy the spores. Each year many fine trees, sound 
except for a slight bruise or other injury, are infected and even- 
tually killed by this fungus. 


Fungi of our Homes. — But not all fungi are found in the open. 
Some have become introduced into our homes and live on some of 
our food or on other materials. These plants are very important 
because of their relation to life in a town or crowded city. An 
example of such a plant is the bread mold (page 222). 

Physiology of the Growth of Mold. — Molds, in order to grow 
rapidly, need food, darkness, oxygen, moisture, and moderate heat. 
They obtain their food from the materials on which they live. 
This they are able to do because the rhizoids give out digestive 
enzymes which change the starch of the bread to sugar and the 
protein to a soluble form which can be absorbed by the cells. 
These absorbed foods are then used to supply energy and make 
protoplasm. Thus molds act like animals, except that digestion 
takes place outside of the body. 

What can Molds live on? — We have seen that black mold lives 
on bread. We find also that it and some other molds (e.g. green or 
blue mold) live upon decaying or overripe fruit. Molds feed upon 
all cakes and breads, upon meat, cheese, and many raw vegetables. 
They are almost sure to grow upon flour if it is allowed to get damp. 
Jelly and other foods containing moisture are particularly favorable 
to molds. Shoes, leather, cloth, paper, or even moist wood will 
give food enough to support their growth. At least one trouble- 
some disease, ringworm, is due to the growth of molds in the skin. 

What Mold does to Foods. — Mold usually changes the taste 
of the material it grows upon, rendering it ^' musty ^^ and some- 
times unfit to eat. Eventually food will be spoiled completely 
because bacterial decay sets in. Some molds are useful. They 
give the flavor to Roquefort, Gorgonzola, Camembert, and Brie 
cheeses. But on the whole, molds are pests which the housekeeper 
wishes to get rid of. 

How to prevent Molds. — As we have seen, moisture is favor- 
able for the growth of mold ; conversely, dryness is unfavorable. 
Inasmuch as the spores of mold abound in the air, materials which 
cannot be kept dry should be covered . Jelly, after it is made, should 
at once be tightly covered with a thin layer of parafiin or waxed 
paper, which excludes the air and possible mold spores. To pre- 
vent molds from attacking fresh fruit, the surface of the fruit 
should be kept dry and, if possible, each piece of fruit should be 



wrapped in paper. Why? Mold spores may be killed in a few 
minutes with dry heat at 212° F. Dry dusting or sweeping will 
raise dust, which usually contains spores of mold and bacteria. 
Use a dampened broom or dust cloth frequently in the kitchen, if 
you wish to preserve foods from molds. 

Other Moldlike Fungi. — Mildews are near relatives of the 
molds found in our homes. Some of them attack leather, cloth, 
etc., in a damp house. Other allied forms do damage 
to plants such as the lilac, rose, and willow. These 
fungi do not penetrate the host plant to any depth 
but cover the leaves of their host with the whitish 
threads of the mycelium and obtain food from the 
outer layer of cells. Hence they may be killed by 
application of some fungus-killing fluid, as Bordeaux 
mixture.^ Among the useful plants preyed upon by 
mildews are the plum, cherry, and peach trees. The 
diseases known as black knot and peach curl are 
caused by similar fungi. 

Among other parasitic fungi are rusts and smuts. 
Smuts attack corn and other cereals and may be 
recognized by the black smutty appearance of the 
mass of ripened spores on the host plant. Wheat 
rust, so called because of the rusty brown appear- 
ance of the wheat attacked by it, is probably the 
most destructive parasitic fungus. It does millions 
of dollars of damage each year to wheat. Indirectly 
this parasite is of considerable importance to city dwellers because 
of its effect upon the price of wheat. 

Fermentation. — It is of common knowledge that the juice of 
fresh apples, grapes, and some other fruits, if allowed to stand 
exposed to the air for a short time, will ferment. That is, the 
sweet juice will begin to taste sour and to have a peculiar odor, 
which we recognize as that of alcohol. The fermenting juice 
appears to be full of bubbles, which rise to the surface. If we col- 

Oat smut, on 
the lower grains. 

A formula for Bordeaux mixture is 

Copper sulphate 1 pound 

Stone lime 1 pound 

Water 10 gallons 



lect enough of the gas in these bubbles to make a test, we find it is 
carbon dioxide. 

Evidently something changed some part of the apple or grape, 
namely, the sugar (C6H12O6), into alcohol (C2H5OH) and carbon 
dioxide (CO2). This chemical process is known as fermentation. 
Yeast. — If a small piece of compressed yeast cake is shaken 
up with some molasses and water and the mixture allowed to 
stand over night, a similar fermentation will take place. Exam- 
ination of a drop of the settlings from the mixture shows that the 

common compressed yeast cake 
contains millions of tiny yeast 
plants. In its simplest form a 
yeast plant is a single cell, 
ovoid in shape and usually 
containing one or more vacu- 
oles. The nucleus is difficult 
to find. Many of the cells 
have others attached to them, 
sometimes several in a row 
(figure, page 223). Such a 

In three fermentation tubes were placed illustrates their method 

equal amounts oi a compressed yeast , 

cake. Then tube A was filled with dis- of reproduction by budding, 
tilled water, tube B with a solution of a_ T?„r„T.»v»« /»««o«o ir^^^^^^ 

, J 4. J 4. ^^ n --t-x. An H/nzyme causes r ermen- 

glucose and water, and tube C with a •' 

nutrient solution containing nitrogenous tation. — It haS been proved 

matter as well as glucose. The quantity ^j^^^ -f g^ ^^^^^ ^^^ grOUnd 

of gas (CO2) m each tube is an index oi . "^ ^ 

the amount of growth of the yeast cells, up Until they are destroyed, the 

take'^piacef^' '^^^ ^^^ ^'^^*''* ^''''^^^ juice filtered from them is able 

to cause fermentation. Sim- 
ilar experiments have been made with bacteria, showing that 
enzymes formed within the cells cause fermentation. These en- 
zymes are called zymases. 

Commercial Yeast. — • Cultivated yeasts are now supplied in 
compressed or dried yeast cakes. In both cases the yeast plants 
are mixed with starch and other substances and pressed into a 
cake. The compressed yeast cake must be used fresh, as the yeast 
plants begin to die rapidly after two or three days. The dried 
yeast cake contains a much smaller number of yeast plants, but 
is probably more reliable if the yeast cannot be obtained fresh. 



Bread Making. — ■ Most of us are familiar with the process of 
bread making. The materials used are flour, milk or water or 
both, salt, a little sugar to hasten the process of fermentation, or 
" rising, '^ as it is called, some butter or lard, and yeast. 

After the materials are mixed thoroughly the bread is put aside 
in a warm place (about 75° Fahrenheit) to " rise." If we ex- 
amine the dough after a few hours, we find many holes in it, 
which give the mass a spongy appearance. The yeast plants, 
owing to favorable conditions, have grown rapidly and made 
bubbles of carbon dioxide. Alcohol is present, too, but this is 
evaporated when the dough is baked. The baking cooks the 
starch of the bread, drives off the carbon dioxide and alcohol, 
and kills the yeast plants, besides forming a protective crust on 
the loaf. 

Sour Bread. — In the ^' rising'^ of bread, bacteria always do 
part of the work of fermentation. Certain of these plants form 
acids after fermentation takes place. The sour taste of the 
bread is usually due to this cause and may be prevented by 
baking the bread before the acids form, by having fresh yeast, 
good fresh flour, and clean vessels with which to work. 

Importance of Yeasts. — Yeasts in their relation to man are 
for the most part useful. They may get into canned substances 
put up in sugar and cause them to " work," giving them a peculiar 
flavor. But they can be easily killed by heating to the temperature 
of boiling. On the other hand, yeast gives us leavened bread, 
which has become a necessity to most of mankind. 

Bacteria cause Decay. — The phenomenon of decay is one of 
the numerous ways in which we can detect the presence of bacteria. 
All organic matter, in whatever form, is sooner or later decomposed 
by the action of untold millions of bacteria which live in water and 
soil. These bacteria are most numerous in rich damp soils con- 
taining large amounts of organic material. They are useful 
because they feed upon dead bodies of plants and animals which 
otherwise would soon cover the surface of the earth to the exclu- 
sion of everything else. Bacteria may thus be considered scav- 
engers. They oxidize organic materials, changing them to 
compounds that can be absorbed by plants and used in building 
protoplasm. Without bacteria and a few of the fungi it would be 



Dead organic matter 

impossible for life to exist on 
the earth, for green plants would 
be unable to get the raw food 
materials in forms that they 
could use in making food and 
living matter. In this respect 
bacteria are of the greatest 
service to mankind. 

Relation of Bacteria to Fer- 
mentation. — Bacteria contin- 
ues the process of fermentation 
begun by the yeasts. In mak- 
ing vinegar the yeasts first make 
alcohol (see page 339), which 
the bacteria change to acetic 
acid. The lactic acid bacteria, 
which sour milk by changing 
the milk sugar to an acid, grow 
rapidly only in a warm temper- 
ature ; hence milk which is 
cooled immediately and kept 
cool or which is pasteurized and 
kept in a cool place will not 
sour readily. Why? These 
same lactic acid bacteria are 

useful when they sour the milk for the cheese maker. 

Other Useful Bacteria. — Certain bacteria give flavor to cheese 

and butter, others give flavor to sauerkraut, while still other 

bacteria aid in the '^ curing " 

of tobacco, in the preparation 

of the dye indigo, in the '^ ret- 
ting" or fermentation of certain 

fibers of plants for the market, 

as hemp, flax, and ramie, in the 

rotting of animal matter from 

the skeletons of sponges, and in 

the process of tanning hides to Microscopic appearance of ordinary 

^ ° milk, showing fat globules and bacteria 

make leather. which cause the souring of milk. 

Soluble Nitrstes 

Dead organic matter is broken down 
by bacteria so that it may be used again 
by green plants. 


Relation of Bacteria to Free Nitrogen. — It has been known 
since the time of the Romans that the growth of clover, peas, 
beans, and other legumes causes soil to become more favorable 
for the growth of other plants. The reason for this has been 
discovered in late years. On the roots of the plants mentioned are 
found little nodules or tubercles ; in each nodule exist millions of 
bacteria, which take nitrogen from the atmosphere and fix it so 
that it can be used by the plant ; that is, they assist in forming 
nitrates which the plants use. Only these bacteria, of all living 
plants, have the power to take free nitrogen from the air and make 
it over into a form that can be absorbed by the roots. They live 
in a symbiotic relationship with the plants on which they form 

Nodules on the roots of the soy bean. They contain the nitrogen-fixing 
bacteria. (Fletcher's Soils.) Copyright by Doubleday, Page and Company. 

tubercles, for the legumes provide them with organic food. All 
the compounds of nitrogen are used over and over again, first by 
plants, then as food by animals, eventually returning to the soil 
again, or in part being released as free nitrogen; but any new 
supply of usable nitrogen must come by means of these nitrogen- 
fixing bacteria. 

Rotation of Crops. — The facts mentioned above are made use 
of by progressive farmers who wish to produce as large crops as 
possible from a given area of ground. Plants that are hosts 
for the nitrogen-fixing bacteria are raised early in the season. 
Later these plants are plowed in and a second crop of a different 
kind is planted. The latter grows quickly and luxuriantly because 
of the nitrates left in the soil by the bacteria which lived with the 

H. NEW CIV. BIOL. — 23 



first crop. For this reason, clover is often grown on land in which 
it is proposed to plant corn later, the nitrates left in the soil giving 
nourishment to the young corn plants. In scientifically managed 
farms, different crops are planted in succession in a given field in 
different years so that one crop may replace some of the elements 
taken from the soil by the previous crop. This is known as rota- 
tion of crops. ^ The an- 

Firsf /ezr 

^^Second year 



nual yield of the average 
farm may thus be greatly 

Five of the elements 
necessary to the life of 
the plant which may be 
taken out of the soil by 
constant use are calcium, 
nitrogen, phosphorus, po- 
tassium, and sulphur. 
Several methods are used 
by the farmer to prevent 
the exhaustion of these 
and other raw food mate- 
rials from the soil. One 
method known as fallow- 
in this rotation of crops, notice that clover is ifig [q tO allow the SOil tO 
used once in three years. This helps to maintain . . ,, ., , 

the supply of nitrates in the soil. remam idle Until bacteria 

and oxidation have re- 
newed the chemical materials used by the plants. This is an expen- 
sive method, if land is high-priced. The more common method 
of enriching soil is by means of fertilizers or materials rich in plant 
food. Manure is most frequently used, but many artificial fertiliz- 
ers, most of which contain nitrogen in the form of some nitrate, are 
used because they can be more easily transported and sold. Such 
are ground bone, guano (bird manure), nitrate of soda, and many 
others. Most fertilizers contain other important raw food ma- 
terials for plants, especially potash and phosphoric acid. Both 
of these substances are made soluble by the action of the carbon 

1 Crop rotation is not only a process to conserve the fertility of the soil, but 
also a sanitary measure to prevent infection of the soil. 


dioxide in the soil, and in this form they can be taken into the 

The Indirect Relation of the Fertility of Soil to the City Dweller. 
— Those of us who live in cities are aware of the importance of 
fresh vegetables brought in from the neighboring market gardens. 
But we sometimes forget that our great staple crops, wheat and 
other cereals, potatoes, fruits of all kinds, our cotton crop, and all 
plants we make use of grow in proportion to the amount of raw 
food materials they take in through the roots. When we remember 
also that many industries within the cities, as mills, bakeries, and 
the like, as well as the earnings of our railways and steamship lines, 
are largely dependent on the abundance of the crops, we may 
recognize the importance of what we have read in this chapter. 

Means of Control of Bacteria in Food Supplies. — We have 
found that bacteria act in two ways upon our food supplies : Di- 
rectly, they feed upon them, causing them to decay ; indirectly, 
they renew our food supplies through this very process of decaj^ 
and by the partnership that exists between the nitrogen-fixing 
bacteria and the legumes. Man, since the time of the Napoleonic 
wars, has won a fight against the spoiling of foods, by discovering 
that heat will kill bacteria in food. Food supplies may be con- 
served by cold storage, canning, and the use of preservatives. 

Cold Storage. — Man has learned to use cold to keep bacteria 
from growing in foods. The icebox at home and cold storage on a 
larger scale enable us to keep foods for a more or less long 
period. If food is frozen, as in cold storage, it might keep without 
growth of bacteria for years. But fruits and vegetables cannot 
be frozen without spoiling their flavor. All frozen foods after thaw- 
ing are particularly susceptible to the bacteria of decay. For 
that reason products taken from cold storage must be used at once. 

Canning. — Canning is simply a method by which first the 
bacteria in a substance are killed by heating and then the sub- 
stance is put into vessels and covered so that no more bacteria can 
gain entrance. In this method of canning often used at home the 
fruit or vegetable is first boiled with salt or sugar, as either of these 
substances aids in preventing the growth of bacteria. The time 
of boiling will be long or short, depending upon the materials to 
be canned. Some vegetables, as peas, beans, and corn, are very 


difficult to can, because spores of bacteria may be attached to them. 
Fruits, on the other hand, are usually much easier to preserve. 
After boiling for the proper time, the food, now free from all bac- 
teria, is put into jars that have been sterilized by boiling. After 
the boiling hot material is poured into the hot jars, they are sealed 
to prevent the entrance of bacteria later. The cold-pack method 
of canning consists in placing fruit or vegetables in the can cold and 
then boiling the cans with their contents, preferably in a pres- 
sure cooker, until all the bacteria are 

Uses of Canning. — Canning as an 
industry is of immense importance to 
man. Not only does it provide him 
with fruits and vegetables at times 
when he could not otherwise get them, 
but it also reduces the cost of such 
things. It prevents the waste of na- 
ture's products at a time when she is 
most lavish with them, enabhng man to 
store them and utilize them later. 
Canning has completely changed the 
life of the sailor and the soldier, who 
Pressure cooker. Steam un- jjj former times used to suffer from va- 

der pressure becomes very not 

and cooks food quickly. Tious discases caused by lack of a proper 

balance of food. 

Preservatives. — A few substances check the development of 
bacteria and in this way preserve the food. Preservatives are of 
two kinds, those harmless to man and those that are poisonous. 
Of the former, salt and sugar are examples ; of the latter, formalde- 
hyde and possibly benzoic acid. 

Sugar. — We have noted the use of sugar in canning. Small 
amounts of sugar are readily attacked by yeasts, molds, and 
bacteria, but a 40 or 50 per cent solution will effectually prevent 
such growths. Preserves are fruits boiled in about their own 
weight of sugar. Condensed milk is preserved partly by the sugar 
added to it ; so are candied fruits. 

Salt. — Salt has been used for centuries to keep foods. Meats 
are smoked, dried, and salted ; some are put down in strong salt 


solutions. Fish, especially cod and herring, are dried and salted. 
The keeping of butter is due to the salt mixed with it. Vinegar 
is another preservative. It, like salt, changes the flavor of mate- 
rials kept in it and so cannot come into wide use. Spices are also 
used as preservatives. 

Harmful Preservatives. — Certain chemicals and drugs, used as 
preservatives, seem to be on the border line of harmfulness. Such 
are benzoic acid, borax, and boracic acid. These chemicals may be 
harmless in small quantities, but. unfortunately in canned goods 
we do not always know the amount used ; also, as a rule, food that 
needs such a preservative is of bad quality in the first place. The 
Pure Food Law makes it illegal to use any of these preservatives 
in food (excepting very small amounts of benzoic acid). Food 
which contains this preservative must be so labeled and should 
not be given to children or people with weak digestion. Unfor- 
tunately, people do not always read the labels, and thus the Pure 
Food Law is ineffective in its working. 

Summary. — The organisms that we call fungi, yeasts, molds, 
and bacteria belong in two great groups, according to their life 
habits. The parasitic forms such as the chestnut blight, the rusts 
and smuts, and many bacteria are parasites and do much harm. 
But a great number of bacteria and fungi, as saprophytes, live on 
dead organic matter and are of incalculable value. Think of a 
world in which no decay takes place, or in which there can be no 
increase in crops. Life would be impossible without the bacteria 
of decay and the nitrifying bacteria, which release simple com- 
pounds of nitrogen for use. Bacteria which harm our foods are 
kept under control by the use of preservatives, sterilization, re- 
frigeration, and canning. 

Problem Questions 

1. Compare the habits of life in saprophytes and in parasites. 

2. Look up outside sources and see how many harmful fungi you can dis- 
cover ; how many useful forms. 

3. How do yeasts and molds obtain food ? How do they digest food? 

4. Sum up the ways in which molds do harm and do good. 

5. Sum up the ways in which yeasts do harm and do good. 

6. Discuss the process of fermentation. 

7. Look up Trench Foot, a disease of the World War. 


8. Leaving the disease-causing bacteria out, are bacteria harmful or useful ? 

9. Explain the nitrogen cycle. 

10. Explain the use of rotation of crops. 

11. In what respect is the cold-pack method of canning superior to the older 
method ? 

12. Distinguish between useful and harmful preservatives. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
At wood. Civic and Economic Biology. P. Blakiston's Son and Company. 
Buchanan, Bacteriology for Students in General and Household Science. The 

Macmillan Company. 
Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 
Conn, Bacteria, Yeasts and Molds in the Home. Ginn and Company. 
Densmore, General Botany. Ginn and Company. 
Gager, Fundamentals of Botany. P. Blakiston's Son and Company. 
Marshall, Microbiology. P. Blakiston's Son and Company. 
Transeau, General Botany. World Book Company. 


Problems : I. To determine the uses of animals : 
(a) Indirectly as food, 
(h) Directly as food. 

(c) When domesticated. 

(d) In yielding raw material for clothing. 

(e) In other direct economic ways. 

(/) In destroying harmful plants and animals. 

II. To determine the harm done hy animals : 

(a) In destroying animals used for food. 

(b) In injuring crops and gardens. 

(c) In injuring fruit and forest trees. 

(d) In destroying stored food and clothing. 

(e) Directly harming man. 

Laboratory Suggestions 

The laboratory portions of this chapter must be largely museum and refer- 
ence work. The work should be varied and opportunity should be given for 
laboratory exercises based on original sources. The pupils should use reports 
of the United States Department of Agriculture, the Biological Survey, vari- 
ous State Reports, and others. 

Special honie laboratory reports may well be made at this time, for example : 
To find out at a local fish market which fish are cheap and fresh at a given 
time. Give reasons for this condition. Study conditions in the meat market 
in a similar manner. Other local food conditions also may be studied. Sur- 
veys can be made of insect pests found in the locality, of the birds which are 
common, of the food the birds eat, and other surveys of a similar nature. 

Indirect Use of Animals as Food. — Just as plants form the food 
of animals, so some animals are food for others. Protozoa and 
many forms of tiny plants, which are swarming near the surface 
of bodies of fresh and salt water, form the food supply of many 
forms of life. These tiny organisms are known collectively as 



plankton. It has been estimated by Professor Forbes that the 
Illinois River, before it was polluted by the Chicago drainage canal, 
produced annually over 150,000,000 pounds of fish food. Almost 
all fish that do not take the hook and that travel in schools or com- 
panies, migrating from one place to another, live largely on plank- 
ton or on smaller fish which feed on plankton. Some fishes as the 
menhaden ^ (bony, bunker, mossbunker of our eastern coast), 
the shad, and others, are provided with gill rakers by means of 
which they strain these minute organisms from the water. Other 
fishes are bottom feeders, as the blackfish and the sea bass, living 
almost entirely upon mollusks and crustaceans. Still others are 
hunters, feeding upon smaller species of fish, or even upon their 
weaker brothers. Such are the bluefish, squeteague or weakfish, 
and others. The whale, the largest of all mammals, strains proto- 
zoa and other small animals and plants out of the water by means 
of hanging plates of whalebone or baleen, the slender filaments of 
which form a sieve from the top to the bottom of the mouth. 

In a balanced aquarium the plants furnish food for the tiny 
animals and some of the larger ones, for example, the snails. The 
smaller animals are eaten by the larger ones. The nitrogen balance 
is maintained through the wastes of the animals and their death 
and decay, furnishing needed materials for the plants. Thus we 
see the marine world is a great balanced aquarium. 

Direct Use of Animals as Food ; Lower Forms. — The forms 
of life lower than the mollusks are of little use directly as food, 
although the Chinese are very fond of certain echinoderms (page 
348), sea cucumbers, which are preserved by drying and are called 
trepang. Sea urchins are eaten in the West Indies, under the name 
of sea eggs. 

Mollusks as Food. — Oysters are never found in muddy locali- 
ties, for in such places they would be quickly smothered by the 
sediment in the water. They are found clinging to stones or on 
shells or other objects which project a little above the bottom, 
in shallow bodies of salt water. 

' Professor Mead of Brown University has discovered that the increase in star- 
fish along certain parts of the New England coast was in part due to over-fishing of 
menhaden, which at certain times in the year feed almost entirely on the young 



The oyster industry is very profitable. Hundreds of boats and 
thousands of men are engaged in dredging for oysters. Three 
of the most important of our oyster grounds are Long Island 
Sound, Narragansett Bay, and Chesapeake Bay. 

Sometimes oysters are artificially '^ fattened " by placing them 
near the mouths of fresh-water streams. Too often these streams 
are the bearers of sewage, and the oyster, which lives on micro- 
scopic organisms, takes in a number of bacteria with other food. 
Thus a person might become infected with the typhoid bacillus 
by eating raw oysters. State and city supervision of the oyster 
industry now makes this possibility very much less than it was some 

Oyster, clam, and scallop. 

years ago, as careful bacteriological analysis of the surrounding 
water is constantly made by competent experts. 

Clams. — Other bivalve mollusks used for food are clams and 
scallops. Two species of the former are known to New Yorkers, 
one as the '^ round," another as the " long " or " soft-shelled " 
clam. The former (Venus mercenaria) was called by the Indians 
*' quahog," and is still so called in the Eastern states. The blue 
area of its shell was used by the Indians to make wampum, or 
money. The quahog is now extensively used as food. The 
'' long " clam {My a arenaria) is considered better eating by the 
inhabitants of Massachusetts and Rhode Island. This clam was 
highly prized as food by the Indians. Dredging for scallops, 
another molluscan delicacy, is an important industry along certain 
parts of the eastern coast. 

Crustaceans as Food. — Crustaceans are of considerable value 
for food. The lobster is highly esteemed as food but has become 
scarce as the result of overfishing. Laws have been enacted in most 
lobster-producing states against overfishing. Egg-carrying lob- 



sters must be returned to the water ; all smaller than six to ten and 
one half inches in length (the law varies in different states) must be 

put back ; other restrictions are placed 
upon the taking of the animals, in hope 
of saving the race from extinction. Such 
states now hatch and care for the young 
lobsters for a period of time ; the United 
States Bureau of Fisheries is also doing 
much good work, in the hope of restock- 
ing to some extent the now almost 
depleted waters. 

Several other common crustaceans are 
near relatives of the crayfish. Among 
them are the shrimp and the prawn, 
thin-shelled, active crustaceans common 
along our eastern coast. In spite of the 
fact that they form a large part of the 
food supply of many marine animals, 
especially fish, they do not appear to be 
decreasing in numbers. They are also 
used as food by man. 

Another edible crustacean of consider- 
able economic importance is the blue 
crab. Crabs are found inhabiting muddy bottoms ; in such local- 
ities they are caught in great numbers in nets or traps baited with 
decaying meat. They are, in- 
deed, among our most valu- 
able sea scavengers, although 
they are hunters of living prey 
also. The young crabs differ 
considerably in form from the 
adult. They undergo a com- 
plete metamorphosis. Imme- 
diately after molting or shed- 
ding of the outer shell in 
order to grow larger, crabs 
are known as '' shedders," or soft-shelled crabs. 
greatly desired by man as an article of food. 

North American lobster. 
This specimen was of unusual 
size and weighed more than 
twenty pounds. 

American Museum of Natural History. 

The edible blue crab. 

They are then 


Honey and Wax. — Honeybees ^ are kept in hives. A colony 
consists of a queen, a female that lays the eggs for the colony; 
the drones, or males ; and the workers. 

The cells of the comb are built by the workers of wax secreted 
by glands in the under part of their abdomens. These cells are 
used by the queen to place eggs in, one egg in each cell. The 
young hatch after three days, and begin life as footless white grubs. 

Beehive with two frames of comb lifted out. 

The young are fed for several days, then shut up in the cells and 
allowed to become pupae. Eventually as adults they break out 
from these cells and take their places in the hive. The young 
workers act first as nurses for the young and later as pollen 
gatherers and honey makers. 

The honeybee gathers nectar, which she swallows, keeping the 
fluid in her crop until her return to the hive. Here it is forced out 
into cells of the comb. It is now thinner than honey. To thicken 
it, the bees swarm over the open cells, moving their wings very 
rapidly, thus evaporating some of the water. A hive of bees makes, 

1 Their daily life may be easily watched in the schoolroom, by means of one of the 
many good and cheap observation hives now made to be placed in a window frame. 
Directions for making a small observation hive for school work can be found in 
Hodge, Nature Study and Life, Chap. XIV. The United States Department of 
Agriculture publishes several excellent pamphlets on the bee and its culture. 

The A B C of Bee Culture, Root, Medina, Ohio, is an excellent little book. 

A book by Snodgrass entitled. The Anatomy and Physiology of the Honey Bee, 
Wiley, is authentic and interesting. 


on an average, between 30 and 80 pounds of honey during a season. 
It is estimated from twenty millions to thirty miUions of dollars' 
worth of honey and wax are produced each year in this country. 

Fish as Food. — Fish are used as food the world over. The 
present value of the yearly catch of the world is estimated at 
$750,000,000. From very early times herring were caught by the 
Norsemen. Fresh-water fish, such as whitefish, perch, pickerel, 

pike, and the various members of the 
trout family, are esteemed food and, es- 
pecially in the Great Lake region, form 
important fisheries. But by far the 
most important food fishes are those 
which are taken in salt water. Here we 
have two types of fisheries : those where 
the fish come up a river to spawn, as the 
salmon, sturgeon, or shad, and those 
where the fish are taken on their feeding 
grounds in the open ocean. Herring are 
the world' s most important catch, though 
not in this country. The salmon of our 
western coast are taken to the value of 
over $40,000,000 a year. Cod fishing 
also forms an important industry ; over 
7000 men being employed and over $30,000,000 of codfish being 
taken each year in this country. 

Hundreds of other species of fish are used as food, the fish that 
is nearest at hand being often the cheapest and best. Why, for 
example, is the flounder cheap in the New York markets ? 

Amphibia and Reptiles as Food. — Frogs' legs are esteemed a 
delicacy. Certain reptiles, as the iguana, a Mexican lizard, are 
used as food by people of other nations. Many of the edible sea- 
water turtles are of large size, the leatherback and the green turtle 
often weighing six hundred to seven hundred pounds each. The 
flesh of the green turtle and of the diamond-back terrapin, an animal 
found in the salt marshes along our southeastern coast, is highly 
esteemed as food. Unfortunately for the preservation of the 
species, these animals are usually taken during the breeding season 
when they go to sandy beaches to lay their eggs. 

Photographed by Dr. 
John A. Sampson. 

Salmon leaping a waterfall 
on the way to their spawning 


Birds as Food. — Birds, both wild and domesticated, form part 
of our food supply. But our wild game birds are disappearing so 
fast that we should not consider them as a source of food. Our 
domestic fowls, turkeys, ducks, etc., form an important food 
supply, and poultry farms give lucrative employment to many 
people. Eggs of domesticated birds are of great importance as 
food, and egg albimiin is used for other purposes, — clarifying 
sugars, coating photographic papers, etc. 

Mammals as Food. — When we consider the amount of wealth 
invested in cattle and other domesticated mammals bred and used 
for food in the United States, we see the great economic importance 
of this class. In 1925, considerably more than $1,000,000,000 
worth of fresh meat was killed in the United States. The United 
States, Argentina, and Australia are the greatest producers of 
cattle. In this country many hogs are raised for food. Their 
meat is used fresh, salted, smoked as ham and bacon, and pickled. 
Sheep, which are raised in great quantities in Australia, Argentina, 
Russia, Uruguay, and this country, are one of the world's greatest 
meat supplies. 

Goats, deer, many larger game animals, seals, walruses, etc., 
are available as food for people in certain parts of the earth. 

Domesticated Animals. — The domestication of the dog, of the 
cow, of the sheep, and especially of the horse, mark epochs in the 
advance of civilization. Beasts of burden are used the world over : 
horses almost everywhere ; certain cattle, as the water buffalo, in 
tropical Malaysia; camels, goats, and the llama in some other 

Man's wealth in many parts of the world is estimated in terms 
of his cattle or his herds of sheep. So many products come from 
these sources that a long list might be given, such as meats, milk, 
butter, cheese, used as food ; wool or other body coverings, 
leather, skins, and hides. Great industries are directly dependent 
upon our domesticated animals, as the tanning of hides, the making 
of shoes, the manufacture of woolen cloth, and many others. 
The total value of all live stock on American farms in the year 
1924 is estimated at the stupendous figure of almost $5,000,000,000. 

Uses of Animal Fibers. — Silk goods are manufactured from 
raw silk, which is a fiber produced by the silkworm, the caterpillar 



of a moth. It lives on mulberry leaves and makes a cocoon from 
which the silk is wound. Chinese silkworms are now raised to a 
slight extent in southern California ; but China, Japan, Italy, and 

France, because of cheap labor, 
are more successful silk-raising 
countries. But the manufac- 
ture of silk goods, from im- 
ported raw silk, is one of our 
great industries. 

There are in this country 
also more than 1000 woolen 
mills, with nearly 200,000 wage 
earners. They produce yearly 
woolen and worsted goods val- 
ued at about $900,000,000. 
These mills use both domestic 
and imported wool. Nearly 
40,000,000 sheep are kept in 
this country. 
Goat's hair, especially that of the Angora and the Cashmere goat, 
camel's hair, and alpaca are much used in the clothing industries. 
Furs. — The furs of many domesticated and wild animals, espe- 
cially the carnivora, are of much economic importance. The 

Silkworms feeding on mulberry leaves. 

Black fox, one of the most valuable fur-bearing animals. 

Alaskan fur seal fisheries, which once amounted to millions of 
dollars annually, have almost ceased because of over-killing, only 


about 16,000 seals being killed in 1923. Otters, skunks, sables, 
weasels, foxes, and minks are of considerable importance as fur 
producers. Even cats are now used, the fur usually masquerading 
under some other name. The fur of the beaver, one of the largest 
of the rodents or gnawing mammals, is now difl&cult to procure, 
but fur of considerable value is obtained from the chinchilla, musk- 
rat, squirrel, and other rodents. The furs of the rabbit and nutria 
are used in the manufacture of felt hats. The quills of the porcu- 
pine (greatly developed and stiffened hairs) have a slight com- 
mercial value. 

Animal Oils. — Whale oil, obtained from the ''blubber" of 
whales, and formerly used for illumination, is now much used for 
lubricating. Neat's-foot oil comes from the feet of cattle and is 
also used in lubrication. Tallow from cattle and sheep, and lard 
from hogs, have so many well-known uses that comment is 
unnecessary. Cod-liver oil is used medically, and much oil is 
obtained also from the menhaden of the Atlantic coast. 

Hides, Horns, Hoofs, etc. — Leather from cattle, horses, sheep, 
and goats is used everywhere. Leather manufacture is one of 
the great industries of the Eastern states, hundreds of millions of 
dollars being invested in manufacturing plants. Horns and 
bones are utilized for making combs, buttons, handles for brushes, 
etc. Glue is made from the animal matter in bones, horns, and 
hoofs. Ivory, obtained from the tusks of the elephant, walrus, 
and other animals, forms a valuable commercial product. It is 
largely used for knife handles, piano keys, combs, etc. 

Perfumes. — The musk deer, musk ox, and muskrat furnish a 
valuable perfume called musk. Civet cats also give us a somewhat 
similar perfume. Ambergris, a basis for delicate perfumes, comes 
from the intestines of the sperm whale. 

Direct Uses of Protozoa. — The protozoa have played an impor- 
tant part in rock building. The chalk beds of Kansas and other 
places are made up to a large extent of the tiny skeletons of pro- 
tozoa, called foraminifera. Some limestone rocks are also com- 
posed in large part of such skeletons. The skeletons of some 
species are used to make a polishing powder. 

Sponges. Coral. — The sponges of commerce have skeletons 
composed of tough fibers of a material somewhat like that of a cow^s 



horn. This fiber is elastic and has the power to absorb water. In 
a hving state, the horny fiber sponge is a dark-colored fleshy mass, 
usually found attached to rocks. The warm waters of the Medi- 
terranean Sea and the West Indies furnish most of our sponges. 
The sponges are pulled up from their resting places on the bottom, 
by means of long-handled rakes operated by men in boats, or they 
are secured by divers. The}^ are then spread out on the shore in 
the sun, and the living tissues allowed to decay ; then after treat- 
ment consisting of beating, bleaching, and trimming, the bath 

sponge is ready for the 

Some forms of coral 
are of commercial 
value. The red coral 
of the Mediterranean 
Sea is the best example. 
Pearls and Mother 
of Pearl. — Pearls are 
prized the world over. 
]\Iost of the finest, how- 
ever, come from che 
oysters and clams in 
the waters around 
Ceylon. If a pearl is 
cut open and examined carefull}^, it is found to be a deposit of the 
mother-of-pearl layer of the shell around some central structure. 
It has been believed that any foreign substance, as a grain of sand, 
might irritate the mantle of the oyster at a given point, thus stim- 
ulating it to secrete around the substance. It now seems likely 
that most perfect pearls are due to the growth within the mantle 
of the clam or oyster of certain parasites which are stages in the 
development of a flukeworm. The irritation thus set up in the 
tissue causes mother of pearl to be deposited around the source of 
irritation, with the subsequent formation of a pearl. 

The pearl-button industry in this country is largely dependent 
upon the fresh-water mussel, the shells of which are used. This 
mussel is being so rapidly depleted that the national government 
has worked out a means for its artificial propagation. 

In some countries little metal images of Buddha 
are placed within the shells of living pearl oysters or 
clams. Over these the mantle of the animal secretes 
a layer of mother of pearl. 



Cochineal and Lac. — Among the many products of insect origin 
is cochineal, a red coloring matter, which consists of the dried 
bodies of a tiny insect, one of the plant lice which live on the 
cactus plants in Mexico and Central America. The lac insect, 
another one of the plant hce, feeds on the juices of certain trees 
in India and pours out a sub- 
stance from its body which 
after treatment forms shellac. 

Gall Insects. — Oak galls, 
growths caused by the sting of 
wasp-like insects, give us prod- 
ucts used in ink making, in 
tanning, and in making pyro- 
gallic acid which is much used 
in developing photographs. 

Other Useful Insects. — 
We have noted that insects 
pollinate flowers; that silk- 
worms spin silk, thus forming 
material for clothing ; that bees 
gather honey; that in many 
cases insects are preyed upon, 
and supply an enormous mul- 
titude of birds, fishes, and 
other animals with food. Dr. 
Forbes of the University of 

Illinois estimates that many of the smaller fresh-water fishes take 
from 99% to 52% insect food, mostly larvse. 

The carrion beetles and many water beetles act as scavengers. 
The sexton beetles bury dead carcasses of animals. Ants in 
tropical countries are particularly useful as scavengers. 

Some forms of animal life are of great importance because of 
their destruction of harmful plants and animals. Insects often do 
a service by eating harmful weeds ; thus many harmful plants are 
kept in check. The '^adybug," or ladybird beetle, is the natural 
enemy of the orange tree scale. It may often be found also feed- 
ing on the plant lice, or aphids, which live on rosebushes. 

A near relative of the bee, called the ichneumon fly, indirectly 

H. NEW CIV, BIOL. — 24 

American Museum of Natural History. 

Pearl shell, and buttons of various sizes 
cut from pearl shell. 


An insect friend of man. An ichneu- 
mon fly boring in a tree to lay its eggs in 
the burrow of a boring insect harmful to 
that tree. 

does man considerable good because of its habit of laying its eggs 

and leaving its young to develop in the bodies of caterpillars 

which are harmful to vege- 
tation. Some of the ichneu- 
mons even bore into trees in 
order to deposit their eggs in 
the larvae of wood-boring 
insects. It is safe to say that 
the ichneumons save millions 
of dollars yearly to this 

Usefulness of the Toad. — 
The toad is of great economic 
importance to man because of 
its diet. No less than eighty- 
three species of insects, mostly 
injurious, have been proved to 
enter into the toad's dietary. 
A toad has been observed to 

snap up 128 flies in half an hour. Thus it could easily destroy 

very many insects during a day and do an immense service to 

the garden during the summer. Toads also feed upon slugs and 

other garden pests. 

Food of Snakes. — Probably 

the most disliked and feared of 

all animals are the snakes. 

This feeling, however, is rarely 

deserved, for, on the whole, our 

common snakes are beneficial 

to man. The black snake and 

the milk snake feed largely on 

injurious rodents (rats, mice, 

etc.), the pretty green snake 

eats injurious insects, and the 

little DeKay snake feeds partly on slugs. If it were not that 

the rattlesnake and the copperhead are venomous, they also 

could be said to be useful, for they devour English sparrows, 

rats, mice, moles, and rabbits. 

The common toad, an insect eater. 



Birds eat Insects. — The food of birds makes them of great eco- 
nomic importance to agriculture in our country. A large part of the 
diet of many of our native birds includes insects harmful to vegeta- 
tion. Investigations undertaken by the United States Department 
of Agriculture (Division of Biological Survey) show that a surpris- 
ingly large number of birds once believed to harm crops really per- 
form a service by killing inj urious insects . Even the much maligned 
crow eats mice and harmful in- 
sects as well as grain and fruit. 
Swallows in the Southern states 
kill the cotton-boll weevil, one of 
our worst insect pests. Our earli- 
est visitor, the bluebird, subsists 
largely on injurious insects, as do 
woodpeckers, cuckoos, kingbirds, 
and many others. The robin, 
whose presence in the cherry tree 
we resent, during the latter part 
of the summer does much good 
by feeding upon noxious insects. 
It has a 95% insect diet until 
June, and after that time about 
40% of its food is insects. Many 
birds vary their diet, using the 
food substances which are most 

abundant around them. The Food of some common birds. Which 

swifts or swallows eat flies, the ^i these birds should be protected by 
, 111* j^ 1 ' man and why ? 

cuckoos and bluejays eat hairy 

caterpillars, which are eaten by few other birds, and much of the 
wmter food of the chickadees consists of eggs of aphids or plant 
lice. Ants are eaten by many species of birds ; beetle larvae are 
preferred by crows, blackbirds, and robins. A pair of nesting" 
robins were observed to dig out and eat from 50 to 70 cutworms 
and earthworms in one day. Many observations of the feeding 
of young birds by their parents indicate that birds eat a large 
amount of food in proportion to their size and consequently 
destroy vast numbers of injurious insects. They are of great 
importance in checking outbreaks of insects. 




Without the birds the farmer would have a hopeless fight against 
insect pests. The effect of killing native birds in great numbers is 
now well seen in Italy and Japan, where insects have increased 
and do great damage to crops and trees. 

Birds eat Weed Seeds. — Not only do birds aid man in his 
battles with destructive insects, but many birds eat the seeds of 
weeds also. Our native sparrows (not the English sparrow), the 
mourning dove, bobwhite, and other birds feed largely upon the 
seeds of many of our common weeds. This fact alone is sufficient 
to make birds of great economic importance. 

Other Useful and Harmful Birds. — Not all birds are seed or in- 
sect eaters. Some, as the cormorants, ospreys, gulls, and terns, are 
active fishers. Near large cities especially gulls act as scavengers, 
destroying much floating garbage that otherwise might be washed 
ashore to become a menace to health. The vultures of India and 
semitropical countries are of immense value as scavengers. Birds 
of prey (hawks and owls) eat living mammals, including many 
rodents ; for example, field mice and rats. 

Of the eight hundred or more species of birds in the United 
States, the only enemies of man are six species of hawks (Cooper's 
and the sharp-shinned hawk in particular), and the great horned 
owl, which prey upon useful birds ; the sapsucker, which kills or 
injures many trees ; the bobolink, which destroys yearly $2,000,000 
worth of rice in the South ; the crow, which feeds on crops as well 
as insects ; and the English sparrow. 

The English Sparrow. — The English sparrow is an example of 
a bird introduced for the purpose of insect destruction, that has 
done great harm because of its relation to our native birds. In- 
troduced at Brooklyn in 1850 for the purpose of exterminating the 
cankerworm, it soon abandoned an insect diet and has driven 
out most of our native insect eaters. Investigations by the United 
States Department of Agriculture show that in the country these 
sparrows and their young feed to a large extent upon grain, thus 
showing them to be injurious to agriculture. Dirty and very 
prolific, they have long since worked their way from the east as far 
as the Pacific coast. In this area the bluebird, song sparrow, 
and yellowbird have all been forced to give way, as well as many 
larger birds of great economic value and beauty. The English 


sparrow has become a national pest, and should be exterminated 
in order to save our native birds. It is feared in some quarters 
that the English starling, which has recently been introduced into 
this country, may in time prove a pest as formidable as the English 

Food of Herbivorous Animals. — We must not forget that other 
animals besides insects and birds help to keep down the rapidly 
growing weeds. Herbivorous animals the world over devour, 
besides the grass which they eat, untold multitudes of weeds, which, 
if unchecked, would drive out the useful occupants of the pastures, 
the grasses and grains. 

Animals Destructive to Other Animals used as Food. — Directly 
or indirectly, animals, either as parasites or not, in their struggle for 
life, destroy quantities of food that man might use. Starfish are 
enormously destructive to young clams and oysters, as the follow- 
ing evidence, collected by Professor A. D. Mead, of Brown Uni- 
versity, shows : A single starfish was confined in an aquarium with 
fifty-six young clams. The largest clam was about the length of 
one arm of the starfish, the smallest about ten millimeters in length. 
In six days every clam in the aquarium was devoured. Hundreds 
of thousands of dollars' damage is done annually to oysters in 
Connecticut alone by the ravages of starfish. During the breed- 
ing season of clams and oysters, the boats dredge up tons of 
starfish which are thrown on shore to die or to be used as fertilizer. 

The liver fluke kills thousands of sheep every year. Tapeworms 
in cattle and trichina in hogs spoil much available food. Round- 
worms parasitize and kill, annually, very many food fish. 

Boring mollusks, such as the whelk, destroy multitudes of other 
mollusks as food. Parasitic insects abound which kill useful 
insects, some of which, like the honeybee, produce food. 

We can hardly estimate the harm done by one-celled parasites 
and their carriers, the ticks, mites, etc., for they are enormously 
destructive to cattle. 

Fish feed upon crustaceans and mollusks. The dogfish, shark, 
and other elasmobranchs destroy many lobsters, crabs, and other 
crustaceans, while many bottom-feeding fish eat mollusks. Fish 
are cannibals also, eating eggs and young of their own kind. 
Salmon eggs are a favorite bait of the western trout. Birds eat 



many fish and much other food, but, as we know, more than com- 
pensate by the good they do. Large numbers of fish are killed 
by minks, otters, seals, and other fishing mammals. It was esti- 
mated that annually $20,000,000 loss to live stock in this country 
was caused by carnivorous animals, such as wolves, coyotes, and 
other flesh-eaters. But this amount is rapidly decreasing. 

±£ow the boll weevil gradually advanced over the Cotton Belt, 1892 to 1922. 

Economic Loss from Insects. — The money value of crops, 
forest trees, stored foods, and other materials destroyed annually 
by insects is beyond belief. It is estimated that they get one 
tenth of the country's crops, at the lowest estimate a matter of 
about 11,000,000,000 yearly. 

Insects which damage Garden and Other Crops. — The grass- 
hoppers and the larvae of various moths do considerable harm 
here, especially the '' cabbage worm," the cutworm, which eats all 
kinds of garden truck, and the corn-ear worm, a pest on corn, 
cotton, tomatoes, peas, and beans. 

Among the beetles which are found in gardens is the potato 
beetle, which eats the leaves of the potato plant. This beetle 
formerly lived upon a wild plant of the same family as the potato, 
and began to infest potato fields when that crop was introduced in 
Colorado, evidently preferring cultivated forms to wild forms of 
this family. 

The one beetle doing by far the greatest harm in this country 


is the cotton-boll weevil. Imported from Mexico, since 1892 it 
has spread over nearly the entire cotton-growing area of the South. 
\\niere '' cotton was king " before the days of the Civil War, many 
Southern farmers have been forced to produce other crops in the 
place of cotton. An example is seen in the decrease of production 
of the once famous sea island cotton. As late as 1916, 117,559 
bales were produced ; in 1924 the record gave only 5 bales ginned. 
The beetle lays its eggs in the young cotton fruit or boll, and the 
larvse feed upon the substance within the boll, thus causing it to 
drop off and, consequently, produce no cotton fiber. It is esti- 
mated that this pest destroys yearly one half of the 
cotton crop, thus indirectly affecting each one 
of us through the increased price of cotton 
goods. The boll weevil, because of the protec- 
tion offered by the cotton boll, is very difficult 
to exterminate. Some weevils are destroyed Cotton-boll weevil : 
by birds, the infected bolls and stalks are burned, ^^"^^ ^^^ ^^^^*- 
millions are killed each winter by cold, other insects are introduced 
to prey on them, but at the present time they are one of the 
greatest pests the South knows. 

The control of this pest seems to depend upon early planting so 
that the crop has an opportunity to ripen before the insects in the 
boll grow large enough to do harm. Various state and govern- 
ment agencies are at work upon the problem, and ultimately the 
boll weevil may do more good than harm by bringing about the 
culture of a type of cotton plant that ripens very early. 

The bugs are among our most destructive insects. The most 
familiar examples of our garden pests are the squash bug; the 
chinch bug, which yearly does damage estimated at $20,000,000, by 
sucking the juice from the leaves of grain ; and the plant lice, or 
aphids. The dreaded phylloxera living on the grape, destroys 
immense numbers of vines in the vineyards of France, Germany, 
and California. 

Insects which harm Fruit and Forest Trees. — Great damage is 
done to trees by the larvae of moths. Massachusetts has already 
spent more than $5,000,000 in trying to exterminate the accident- 
ally imported gypsy moth. The codling moth, which bores into 
apples and pears, is estimated to ruin yearly $3,000,000 worth of 



Pholo by Davison. 

Female tussock moth which 

it has deposited more than two 
hundred eggs. 

fruit in New York alone, which is only one of the important apple 
regions of the United States. Among these pests, the most im- 
portant to the dweller in a large city is the tussock moth, which 

destroys our shade trees. The cater- 

pillar may easily be recognized by its 

^^^ hair}^, tufted body and red head. The 

\ nb^ eggs are laid in what look like masses 

V. ^k _,.^C of foam on the outside of the cocoon 

N|fi&|B ^f^A attached to the bark of a shade tree 

^^^ ^H^ (see the figure). By collecting and 

^W^ ^^ burning the egg masses in the autumn, 

^ we may save many shade trees the 

following year. 

has just emerged from the The larvsB^ of some moths damage 

cocoon at the left, upon which trees by boring into the wood of the 

tree on which they live. Such are the 
peach, apple, and other fruit-tree 
borers common in our orchards. Some kinds of beetles pro- 
duce boring larvae which eat their way into trees and kill thou- 
sands of forest and shade trees annually. The hickorj- borer 
threatens to kill all the hickory trees in the Eastern states. 

Among the bugs most de- 
structive to trees are the scale 
insect and the plant lice. The 
San Jose scale, a native of 
China, was introduced into the 
fruit groves of California about 
1870 and has spread all over 
the country. 

Insects of the House or Store- 
house. — Weevils are the great- 
est pests, frequentl}^ ruining tons 
of stored corn, wheat, and other 
cereals. Cockroaches will eat almost any kind of breadstuff s as 
well as clothing. The carpet beetle is a recognized foe of the house- 
keeper ; the larvae feed upon all sorts of woolen material. The 
larvai of the clothes moth do an immense amount of damage, 
especially to stored clothing. Fleas, lice, and bedbugs are among 









Photo by Davisou. 

Caterpillar of tussock moth. 


man's personal foes. Besides being unpleasant, they are believed 
to be disease carriers, and as such they should be exterminated.-^ 

How the Harm done by Insects is controlled. — The combating 
of insects is directed by several bodies of men, all of which have 
the same end in view. These are the Bureau of Entomology of 
the United States Department of Agriculture, the various state 
experiment stations, and medical and civic organizations. 

The Bureau of Entomology works in harmony with the other 
divisions of the Department of Agriculture, giving the time of its 
experts to the problems of controlling insects which, for good or 
ill, influence man's welfare in this country. The destruction of 
the malarial mosquito and the control of the typhoid fly; the 
destruction of harmful insects by the introduction of their natural 
enemies, plant or animal ; the perfecting of the honeybee ; and the 
introduction of new species of insects to pollinate flowers not native 
to this country (see Blastophaga, page 38), are some of the problems 
to which these men have devoted their time. 

All the states and territories have, since 1888, established state 
experiment stations, which work in cooperation with the govern- 
ment in the war upon injurious insects. These stations are often 
connected with colleges, so that young men who are interested in 
this kind of natural science may have opportunity to learn and to 

The good done by these means directly and indirectly is very 
great. Bulletins are published by the various state stations and 
by the Department of Agriculture, most of which may be ob- 
tained free. The most useful of these from the high school stand- 
point are the Farmers^ Bulletins, issued by the Department of 

Rats as Pests. — David E. Lantz of the Bureau of Biological 
Survey is authority for the statement that the rat is the most 
destructive mammal in the world. He estimates the actual money 
loss from destruction of property by rats each year in this country 
to be over $200,000,000. Rats destroy the timber in houses, they 
cause fires by gnawing matches, they destroy great quantities of 
standing grain and stored food, they kill myriads of young chickens 

^ Directions for the treatment of these pests mp,y be found in pamphlets issued 
by the United States Department of Agriculture. 



and other poultry and untold numbers of young birds. Worst of 
all, they carry diseases, especially bubonic plague. The fighting of 
rats alone, in the epidemics of plague in this country, has cost mil- 
lions of dollars. They can be and must be exterminated. Here is 
good material for a project report : How shall we exterminate rats? 
Cats. — Many cats are kept as pets, and many run wild. Cats 
of both kinds do much injury by killing birds. They also carry 
disease germs. 

Animals that prey upon Man. — The toll of death from animals 
which prey upon or harm man directly is relatively small. Snakes 
in tropical countries kill many cattle and not a few people. 

The bite of the rattlesnake of our own country, although danger- 
ous, seldom kills. The dreaded cobra of India has a record of over 
250,000 persons killed in thirty-five years. The loss of life from 
snake bites should soon be much reduced, thanks to the man- 
ufacture of antitoxin serums made to counteract the venom of 
poisonous snakes. The Indian government yearly pays out large 
sums for the extermination of venomous snakes, over 200,000 of 
which have been killed during a single year. 

Alligators and crocodiles feed not only on fishes, but often 
attack large animals, as horses and cows, and even man. They 

seek their prey chiefly at 
night, and spend the day 
basking in the sun. 
The crocodiles of the 
Ganges River in India 
levy a yearly tribute of 
many hundred lives 
from the natives. 

Carnivorous animals 
which are not domes- 
ticated, such as lions 
and tigers, still inflict damage in certain parts of the world, but 
as the tide of civilization advances, their numbers are slowly but 
surely decreasing, so that as important factors in man's welfare 
they may be considered almost negligible. 

Summary. — Man has made use of many animals for food, for 
clothing, and in numerous other ways. His food and other supplies 

A flesh-eating reptile, tlie alligator. 


are increased by certain animals that destroy others that feed upon 
or otherwise destroy man's commodities. We have learned also 
some of the ways in which these destructive animals work. We 
see the toll taken by destructive animals, insects in particular, so 
great that one tenth of the fruit of man's labors is wasted. But 
we learn also that this destruction is all a part of the life which 
animals lead in order to exist. They are the destructive force on 
the earth, using the products built up by the green plants. 

Problem Questions 

1. What is plankton and of what use? 

2. What lower animals are directly of use as food? 

3. Why are lobsters and other shellfish being exterminated? 

4. How do fish compare in economic importance with other animals which 
are used as food? 

5. State the uses of birds. List different birds according to the good they 

6. List all the animal products used as food and as clothing. Other uses? 

7. List animals destructive to food and show how each does harm. 

8. In what indirect way has the cotton-boll weevil done good ? 

9. What useful insects can you name, and why are they useful? 

10. What are the agencies which help to control the harm done by anima's? 
Show how these agencies work. 

11. Why is the rat marked for extermination? Can you list any other 
animal pests to go with the rat ? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Folsom, Entomology. P. Blakiston's Son and Company. 

Herrick, Household Insects and Methods of Control. Cornell Reading Course. 

Hornaday, Our Vanishing Wild Life. New York Zoological Society. 

Hodge, Nature Study and Life. Ginn and Company. 

Reese, Economic Zoology. P. Blakiston's Son and Company. 

Stone and Cram, American Animals. Doubleday, Page and Company. 

Toothaker, Commercial Raw Materials. Ginn and Company. 

Hornaday, The American Natural History. The Macmillan Company. 

Jordan and Evermann, American Food and Game Fishes. Doubleday, Page 

and Company. 
Shaler, Domesticated Animals. Charles Scribner's Sons. 
Farmers' Bulletins, 513, 630, 740, 801, 1294, 1326, 1346, 1353, 1371. 


Problems : What is conservation and why is it necessary? 

What are some of the methods of conservation? 

How may our forests be conserved ? 

How may we protect our food fishes ? 

How may we conserve our bird life ? 

What are some of the problems in the conservation of mammals ? 

Laboratory Suggestions 

Field or museum trip to study some problems of conservation in my 

Home project. Bird census made by the members of the class as individual 

Home project. Survey of the natural resources of my community. An excel- 
lent method is for the individual members of the class to report on the different 
phases of the conservation movement as it affects life in their community. 

Meaning and Need of Conservation. — Ever since President 
Roosevelt gave his energy to the conservation movement, we have 
heard a good deal about the conservation of our natural resourced. 
Conservation means protection or care of the natural gifts that 
nature has given us. More than this, it involves the fullest possible 
development of our natural resources. But why is conservation 
so necessary? 

We have seen that life on this earth is give and take, that animals 
and plants live in a balanced relationship, and that if this balance 
is disturbed, something is sure to happen to some of the living 
things. Examples of such disturbances were seen when the rabbit 
was introduced into Australia and the English sparrow into this 
country. Having no natural enemies, they multiplied rapidly, 
crowded out other useful animals, and became pests. Examples 
in the plant world are seen in the introduction of such pests as the 
Russian thistle and other weeds. 



Man^s Need of Conservation. — Man's domination of the 
civilized world has meant, as he multiplied, the necessity of more 
food, more water and better water supplies, more power to light 
his cities and run his machines, more fuel, and in fact more of 
everything necessary to his complex life. The balance of nature 
has been disturbed by man in his ever increasing demand for food 
and other supplies. In consequence, he must learn how to con- 
serve the supplies so necessary to him. It is certainly the place 
of a course in Civic Biology to show the average citizen how and 
why this may be done. 

Methods of Conservation. — Although in biology we are not 
directly concerned with methods of conservation which deal with 
our mines or our fuel oil, we are indirectly studying the con- 
servation of water supplies when we deal with the problem of the 
protection of our forests. Our national health is the largest 
problem of conservation with which we have to deal, and some 
methods have been discussed in earlier chapters. This chapter 
is concerned particularly with the conservation of useful plants 
and animals. This gives us two general methods to consider: 
first, how to protect our useful plants and animals ; second, how 
to eliminate harmful organisms. 

Methods of Forest Conservation. — Back of all life on the earth 
are the food supplies made by the green plants. Back of our water 
supplies and our rich soil lie our forests. We have already seen 
that the forest is being used more than four times as fast as it 
grows s and that our forest areas are lessening each year. We 
already lack hardwoods for trim and furniture and our pulp wood 
reserves are dwindling rapidly. 

Avoiding Waste. It is evident that we must replant our forests 
as they are used and plant new areas, and that we must obtain 
substitutes for some of the forest products, and make use of waste 
products from the forests. Formerly, lumber companies burned 
the sawdust and other waste from the mills; now fuel alcohol 
and other valuable products are obtained from them. It is esti- 
mated that more than 300,000,00Q gallons of fuel alcohol could be 
made annually from the wood thus wasted. It is estimated that 
20% of the timber now wasted might be used in building. Rail- 
roads use 15% of our timber for ties ; treatment of these ties with 


creosote or other chemicals would result in the annual saving of 
1,500,000,000 board feet. Substitutes are being found for boxes, 
which take a very large amount of cut lumber. And since it is 
estimated that 25% of a tree in the forest is lost in the cutting and 

Courtesy of United States Forest Service. 

Destructive lumbering in Colorado. 

40% is wasted in the mill, it is evident that less wasteful methods 
will conserve a large amount of the lumber now lost. 

New Forest Areas. State forestry stations and the national 
government are reforesting cut areas, and many lumber companies 
have begun to follow their example. Railroads annually are 
planting thousands of young trees. Farmers have begun to 
realize that the high price of lumber makes a wood lot often more 
productive than other areas of similar size on the farm. Forestry 
is becoming more and more a practical business, hundreds of young 
men going out from schools of forestry each year, prepared to help. 
If we all do our share, the forests will be saved. But we must 
begin now. 

The Conservation of Fresh-water Fishes. — In another place we 
have seen that the food supply of many of our fishes depends upon 
the plankton, tiny plants and animals which swarm near the surface 
of bodies of water. In many parts of the United States these little 
organisms have been exterminated, and the food fish with them, by 
the pollution of our streams and lakes. If crude sewage is dis- 


charged into a river untreated, the organic matter absorbs much 
or all of the dissolved oxygen in the water. But this oxygen is 
absolutely essential for plant and animal life. Oil wastes poured 
out by oil-burning steamers are becoming a nuisance along our 
shores and are responsible for the death of many food fish. If 
our fish and other water animals are to be preserved, we must 
stop the pollution of our national waterways. Dr. Henry B. Ward 
is authority for the estimate that if rivers now polluted with sewage 
and factory wastes were clean again they would put $100,000,000 
a year into the pockets of taxpayers from the sale of marketable 
fish. In addition to this would be the sport of thousands of fisher- 
men and other thousands who would use the rivers for boating 
and bathing. 

The Conservation of Shellfish. — The problem of conserving 
shellfish is concerned in part with the extermination of their 
natural enemies. If we could kill off all starfish and boring mol- 
lusks, the oysters and clams would be much more plentiful. But 
over-fishing is the most important danger. The oysters of Chesa- 
peake Bay were thought inexhaustible until they were almost 
fished out. Then the state of Maryland discovered that oyster 
culture was necessary if this great asset was to be preserved. 

Oysters pass the first few days of their existence as free swimming 
larvae. Then they settle on the bottom, and if they do not find 
some solid object which raises them above the mud of the bottom, 
they will die. Oysters are now protected by cultivation ; on the 
bottom, in certain areas of shallow water, are placed bunches of 
twigs, broken rocks, or old oyster shells to which the young oysters 
attach themselves. After they have grown to approximately the 
size of a quarter or half dollar these '' seed " oysters are spread over 
the bottom of the oyster beds, and later are harvested. 

Clams and scallops have been nearly depleted in some areas, 
and it has become necessary to conserve the supply by having 
closed seasons and by transplanting the " soft clam " of the east 
to the Pacific Coast, where it thrives. 

Lobsters are being conserved by taking the fertilized eggs and 
raising the young in hatcheries until they are large enough to care 
for themselves. This artificial protection lasts only while they are 
free swimming larvse. 



Conservation of Ocean Fishes. — We have just seen that the 
relation of fish Hfe to their natural food is an important factor in 
preserving our supply of fish, especially in inland waters. The 
balance of life is equally important for fish in the ocean. It is 
one of the greatest problems of our Bureau of Fisheries to discover 
the relation of various fishes to their food supplies so as to aid in 
the conservation of life in our lakes, rivers, and seas. 

Migration of Fishes. — Some fishes change their habitat at dif- 
ferent times during the year, moving in vast schools northward in 
the summer and southward in the winter. In a general way such 

migrations follow the 
coast lines. Examples 
of such migrator}^ fish 
are the cod, menhaden, 
herring, and bluefish. 
The migrations are 
due to temperature 
changes, to the quest 
of food, and to the 
spawning instinct. 
Salmon and some other 
fish pass up rivers to 
spawn ; the eel, on the 
contrary, leaves the 
rivers and spawns in 
the ocean. Some fish 
migrate to more shal- 
low water in the sum- 
mer, and to deeper water in the winter ; here the reason for the 
migration is doubtless the change in temperature. All of these 
habits are studied by the fishermen, who are thus able to catch fish 
where and when they are most plentiful. The cod and herring 
fisheries are notable examples. 

The Egg-laying Habits of the Bony Fishes. — The eggs of most 
bony fishes are laid in great numbers, varying from a few thousand 
in the trout to many hundreds of thousands in the shad and several 
millions in the cod. The time of spawning is usually spring or 
early summer. After the eggs are laid the male fish usually 

Development of a trout. 1, the embryo within the 
egg ; 2, the young fish just hatched, with the yolk 
sac still attached ; 3, the young fish. 


deposits milt, consisting of millions of sperm cells, in the water 
just over the eggs, and fertilization follows. Some fishes, as 
sticklebacks, sunfish, toadfish, etc., make nests, but usually the 
eggs are left to develop by themselves, sometimes attached to some 
submerged object, but more frequently free in the water. In 
some eggs a tiny oil drop buoys up the egg to the surface, where 
the heat of the sun aids development. Both the eggs and young 
fish are exposed to many dangers ; they are eaten, not only by 
birds, fish of other species, and other water inhabitants, but also 
by their own relatives and even parents. Consequently, a very 
small percentage of eggs ever reach maturity. 

The Relation of the Spawning Habits to Economic Importance 
of Fish. — The spawning habits of fish are of great importance to 
us because of the economic value of fish to mankind, not only 
directly as a food, but also indirectly as food for other animals in 
turn valuable to man. Many of our most desirable food fishes, 
notably the salmon, shad, sturgeon, and smelt, pass up rivers from 
the ocean to deposit their eggs, swimming against strong currents 
much of the way, some species leaping rapids and falls, in order 
to deposit their eggs in localities where the conditions of water 
and food are suitable and the water is shallow enough to allow 
the sun's rays to warm it sufficiently to cause the eggs to develop. 
The Chinook salmon of the Pacific Coast, w^hich is used in the 
Western canning industry, travels over a thousand miles up the 
Columbia and other rivers, to the headwaters where it spawns. 
The salmon begin to pass up the rivers in early spring, and reach 
the spawning beds, shallow deposits of gravel in cool mountain 
streams, before late summer. Here the fish, both males and 
females, remain until the temperature of the water falls to about 
54° Fahrenheit. The eggs and milt are then deposited, and the 
old fish die, leaving the eggs to be hatched out later in the water 
warmed by the sun. 

The instinct of salmon and other species of fish to go into shallow 
rivers to deposit their eggs has been made use of by man. At 
the time of the spawning migration the salmon are taken in vast 
numbers, to the value of over $40,000,000 annually. 

Need of Conservation. — The need for conservation of this 
important national asset is great. The shad within recent times 

H. NEW CIV. BIOL. — 25 



have abandoned their breeding places in the Connecticut River, 
and the salmon have been exterminated along our eastern coast 
within the past few decades. Onh' a few years hence, the Western 
salmon will be extinct if fishing is continued at the present rate. 
More fish must be allowed to reach their breeding places. 

The sturgeon, the eggs of which are used in the manufacture of 
the delicacy known as caviar, is an example of a fish that is almost 
extinct in most parts of the world. Shad have almost disappeared 
from our Eastern rivers because they are caught during their 
breeding season and their eggs used for food. Other food fish 
taken at the breeding season are also in danger. 

Fortunately, the government through the Bureau of Fisheries, 
and various states by wise protective laws and by artificial propa- 
gation of fishes, are begiiming to turn the tide. Certain days of 
the week the salmon are allowed to pass up the Columbia un- 
molested. Obstructions must be removed which might prevent 
fish from passing up or down rivers. Closed breeding seasons 

protect our trout, bass, 
and other game fish ; also 
the catching of fish under 
a certain size is pro- 

Artificial Propagation 
of Fishes. — IMany fish 
hatcheries, both govern- 
ment and state, are en- 
gaged in artificial!}^ fertil- 
izing millions of fish eggs 
of various species and 
protecting the young fry 
until they are of such size 
that they can take care 
of themseh'es, when they are placed in ponds or streams. For 
artificial fertilization the ripe eggs from a female are first squeezed 
out into a pan of water ; in a similar manner the milt or sperm 
cells are obtained, and poured over the eggs. After the eggs are 
thus fertilized, they are placed in receptacles supplied with running 
water and left to develop under favorable conditions. Shortly 

Courtesy of New York State Conservatio/i Cjmnnssion. 

Artificial fertilization of fish eggs. (See text 


after the egg has segmented (divided into many cells) the embryo 
may be seen developing on one side of the egg. The rest of the 
egg is made up of food or yolk and when the baby fish hatches 
it has the yolk attached to its ventral surface for some time. 
Eventually the food is absorbed into the body of the fish. (Figure, 
page 372.) The young fry are kept under ideal conditions until 
later, when they are shipped, sometimes thousands of miles, t( 
their new homes. 

Reasons for Conservation of Birds. — We have already learned 
that birds, with few exceptions, are of very great value to man, 
through their destruction of weed seeds and of insects harmful to 
crops. But in spite of this fact, many species of birds have been 
almost exterminated in this and other countries, and the total 
number of birds has decreased to an alarming extent. This has 
been due largely to killing for food and " sport," and for plumage. 
A few decades ago, the spraying of trees was unknown ; to-day 
$10,000,000 or more a year is spent for labor and sprays ! It is 
estimated by Dr. Hornaday of the New York Zoological Park, that 
a yearly toll of $520,000,000 now collected by insects might be 
saved if we had as many birds as formerly. 

The American passenger pigeon, once very abundant in the 
Middle West, is now extinct. Audubon, the greatest of all Ameri- 
can bird lovers, gave a graphic account of the migration of a flock 
of these birds. So numerous were they that when the flock rose 
in the air the sun was darkened, and at night the weight of the 
roosting birds broke down large branches of the trees in which they 
rested. To-day not a single specimen of this pigeon can be 
found, because they were slaughtered by the hundreds of thousands 
during the breeding season. The wholesale killing of the snowy 
egret to furnish ornaments for ladies' headwear is another example 
of the improvidence of our fellow-countrymen. It was killed 
during its breeding season ; and for every egret killed, an entire 
bird family was blotted out of existence. Prairie chickens are 
unknown in many states where they were abundant before 1900. 
The same thing will happen to the quail where it is unprotected. 

Hawks, owls, shrikes, crows, and jays all play a small part in the 
destruction of our native birds. The English sparrow has done 
great harm in driving away useful birds. Squirrels and particu- 



Nesting boxes will attract 
and protect birds. 

larly rats are very destructive of eggs and young birds. Small 
boys, with air guns, and foreigners who kill for food, are responsible 
for the death of many birds. But according to Forbush, the house 
cat is the worst enemy of our feathered friends. He estimates 
from many observations that the average pet cat kills at least 
50 birds a year. Assuming that the cat kills only ten birds a year, 
and that there is one cat to each farm in Massachusetts, there 
would be 700,000 birds annually killed by 
cats in that state. Think of what this 
means for the entire United States ! 

Home Conservation Methods. — Nesting 
boxes can be easily made and are a great 
asset for a home. Birds are delightful as 
well as useful neighbors. Wrens are often 
attracted with boxes having small holes 
not larger than one and one eighth inches in 
diameter. Place the boxes so that cats can- 
not get access to them. During the winter 
birds may frequently be preserved by feed- 
ing. Suet baskets and nuts put on shelves placed in trees and 
inaccessible to cats are the best means. Bird baths also are means 
of attracting birds. 

Bird Migrations in Relation to Conservation. — It has long 
been known that certain birds breed in the far north and spend 
the winter in the tropics. The golden plover is the most notable 
example, for it nests in the Arctic and winters in southern South 
America, making a yearly round trip of more than 16,000 miles. 
Wild ducks and geese are examples of game birds that make these 
pilgrimages each year. The bobolink migrates from the northern 
part of our country to a tropical part of South America, It is 
largely due to this migratory instinct that many of our birds have 
been subject to slaughter by hunters. Many states have laws 
which allow the killing of large ''bags " of ducks and other game 
birds and do not sufficiently protect migrating birds. It has been 
estimated that 5,000,000 hunters go out every season for birds or 
other animals. Thanks to the treaty of 1916 with Great Britain, 
more than 500 kinds of migrating birds are protected in this country 
and Canada from capture, killing, or sale. All over this country, 



owing to the work of the Audubon Society and of Dr. Hornaday 
and other leaders, we have awakened to the fact that our birds 
are valuable assets. Now it is against the law to kill either game 
birds during the breeding season or most wild birds at any time. 





Bobolink, male, in spring. 

The bobolink summers and breeds in the north, where its diet is largely insects. 
It spends the winter far south of central South America. Eastern and western 
limits of the migration routes are shown by dashed lines in the map. On its way 
south the bobolink does great damage to the rice crop. 

Other Means of Conservation. — Fortunately for the average 
citizen, some public-spirited people who have money are willing 
to spend it for the common good. Not only are there many pri- 
vate game preserves in various parts of the country, but also sev- 
eral bird sanctuaries have been established, notably Marsh Island 
and Avery Island, both in Louisiana. Private game and bird 
refuges and preserves are estimated to contain nearly 800,000 acres 
in this country and over 150,000 acres in Canada. In addition to 
this, the United Sta.tes Government has created a total of nearly 
sixty bird refuges (map, page 378). 

Conservation of Mammals. — It was not so many years ago that 
the people of this country thought the vast herds of buffalo that 
covered the Western plains were inexhaustible ; but ten years of 
systematic killing nearly exterminated them. To-day a few thou- 



sand exist, protected by law ; and they would have gone had it 
not been for the fact that the buffalo breeds in captivity. The 
same story may be told of the Alaska fur seal, almost exterminated 
a few years ago by over hunting and now protected by law. As 
time goes on and the furs of wild animals become scarcer and 
scarcer through over killing, we find more and more imperative the 
need for protection and conservation of many of these fast-vanish- 
ing wild forms. Already, breeding of some fur-bearing animals 
in captivity has been tried with success, and substitutes for wild 
animal skins are coming more and more into the markets. Black 
and silver fox raising has been tried successfully in many parts of 
this country and Canada, $2500 to $3000 being given for a single 
animal. Skunks, martens, and minks are also being bred for the 
market. At last partly awake to our duty toward the wild 
mammals of this country, the government has made some wise 
laws and established a few reservations in our National Parks, 
so that the future for wild life in this country is safer. 


1 *''^Tr^""~~^~~~-^-.-_ 


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/W-\ "'" 


/~-vy.~!/ '/~U~^. — : 





V yTn~p 

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■y Zs- 


^ — \ ' / • 


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Map showing location of national bird reservations (•) and national 
game reservations (o) . 

Summary. — Conservation is necessary because we must save 
our forests and our rapidly vanishing wild life from destruction. 
Countries where conservation is not practiced show increasing 
depredations by insects because of the lack of bird life, and desert 


wastes devoid of any life. The balance of life, disturbed by man, 
must be artificially adjusted. This can be done only by protecting 
those weak species which are helpful and destroying the harmful 
plants and animals. 

Problem Questions 

1. Why is conservation needed ? 

2. What forest reserves, if any, do you have in your state? What laws do 
you have in your state which are aimed to protect the water supply ? 

3. Are there any individual examples of the conservation of forest or forest 
supplies in your community? Be specific. 

4. Why is stream pollution an important factor in conservation? 

5. Describe some methods for the conservation of shellfish. 

6. Why do fish migrations play an important part in their conservation 
or destruction ? What is your state doing to conserve fish life ? 

7. What are some important factors in the destruction of bird life? 

8. Why are bird migrations important from the standpoint of conservation ? 

9. Report on the game laws in your state. Are they adequate to protect 
the fish and the birds ? 

10. Discuss the good and bad points in owning a cat. 

11. How may we attract birds about our homes? Make this a project 

12. What wUd mammals are found in your state ? T\Tiat is being done for 
their conservation? 

Problem and Project References 

Articles in Outdoor America, National Association of Audubon Society pub- 
lications and Yearbooks of the United States Department of Agriculture. 

Chapman, Bird Life. D, Appleton and Company. 

Forbush, Useful Birds and Their Protection. Massachusetts Board of Agri- 

Hornaday, Our Vanishing Wild Life. New York Zoological Society. 

Hornaday, Wild Life Conservation in Theory and Practice. Yale University 

Trafton, Bird Friends. Houghton Mifflin Company. 

Weed and Dearborn, Birds in Their Relations to Man. J. B. Lippincott Com- 

Farmers' Bulletins: 493, 513, 609, 621, 630, 1239. 





Problems: To determine what makes the offspring of animals or 
of plants tend to he like their parents. 

To determine what makes the offspring of animals or of plants 
differ from their parents. 

To learn about some methods of plant and animal breeding. 

(a) By selection. 

(b) By hybridizing. 

(c) By other methods. 

Suggestions for Laboratory Work 

Laboratory exercise. On variation and heredity among members of ii 
class in the schoolroom. 

Laboratory exercise. On the construction of a curve of variation in measure- 
ments from given plants or animals. 

Laboratory demonstration. Stained egg cells (ascaris) to show chromosomes. 

Laboratory demonstrations. To illustrate the part played in plant and 
animal breeding by (a) selection ; (b) hybridizing ; (c) budding and grafting. 

Heredity and what it means. — As you look at the boys in 
your class, you notice that each boy seems to be more or less like 
every other boy ; he has a head, body, arms, and legs, and even in 
minor ways he resembles each of the other boys in the room. 
Moreover, if you should ask any particular boy, no doubt he 
would tell you that he resembled in certain respects his mother or 
his father. If you should ask his parents whom he resembled, 
they would say, '' We can see his grandfather (or his grandmother) 
in him." 




The law of nature which causes a child to possess characters 
Hke either or both of his parents and like their parents as well, 
is called heredity. If we trace the workings of heredity in our own 
individual cases, we shall probably find that we are molded like 
our ancestors not only in physical characters but also in mental 
qualities. The ability to play the piano well or to paint well is 
probably as much a case of inheritance as the color of one's eyes or 
the shape of one's nose. We are a complex of physical and mental 
characters, received from 
all our ancestors. 

Variation. — But no boy 
in the class is exactly like 
any other boy; even 
brothers are different in 
appearance and in action. 
In this wonderful mold of 
nature each one of us 
tends to be slightly dif- 
ferent from his or her 
parents. Each plant, each 
animal, varies to a greater 
or lesser degree from its 
immediate ancestors, and may vary to a great degree. This ten- 
dency among plants and animals is called variation. Heredity 
and variation are the corner stones on which all the work in the 
improvement of plants and animals, including man himself, is 

The Bearers of Heredity. — We have seen that a cell contains 
a nucleus, in which are certain very minute structures known as 
chromosomes (because they take up color when stained). When 
cells divide, each chromosome divides by splitting lengthwise, so 
that equal amounts of each chromosome are thus carried into the 
new cells formed from the original cell. These chromosomes are 
believed to be the structures which contain the determiners of the 
qualities which may be passed from parent to offspring ; in other 
words, the qualities that are inheritable (see pages 47-49, 396). 

The Germ Cells. — But it has been found that certain cells of 
the body, the egg and the sperm cells, before uniting contain only 

Example of variation in heads of roosters. 

Certain cells in the body of an animal are set apart very early to become sex cells 
called gametes. The cells that do this may be called sperm mother cells or e^ 
mother cells. These divide many times, by mitosis (page 48). Next comes a perioc 
of growth, when the cells become very large. Then comes reduction division. In- 
stead of mitosis, the cell splits and only half the number of the chromosomes (pages 
46 and 396) go with each part. In the male after another division by mitosis the cy- 
toplasm stretches out into a long motile tail and the mature male gamete is called the 
sperm. During reduction division in the female, the cell splits into unequal parts,! 
each taking half the number of the chromosomes. The small structure is called the 
polar body. As a result of further division another polar body is thrown off; an( 
the remaining cell becomes a mature egg. Fertilization follows. 



half as many chromosomes as do the body cells.^ In preparing 
for the process of fertilization, half of these elements have been 
eliminated, so that when the egg cell and the sperm cell are united 
they will have the same number of chromosomes as the other cells 
of the body. 

We have already learned that in the process of fertilization the 
nuclei of the sperm and of the egg cell unite, or fuse, to form a new 
nucleus in the fertilized egg. If the chromosomes carry the deter- 
miners of the characters which are inheritable, then it is easy to 
see that a fertilized egg must contain equal numbers of chromo- 
somes from the bodies of both parents. In this way characters 
from each parent are handed down to the new individual. 

Offspring are Part of their Ancestors. — If you receive charac- 
ters from your parents and they received characters from their 
parents, then you must have some of the characters of the grand- 
parents, and as a matter of fact each of us does have some traits or 
lineaments which can be traced back to a grandfather or grand- 
mother. Indeed, as far back as we are able to go, ancestors have 
contributed something. 

Natural Selection. — Charles Darwin was one of the first 
scientists to suggest how heredity applies to the development of 
plants and animals. He knew that although animals and plants are 
like their ancestors, they also tend to vary. In nature, he believed, 
the variations which best fit a plant or animal for life in its own 
environment are the ones which are handed down, because those 
individuals having variations not fitted for life in that particular 
environment will die. Thus, said Darwin, nature seizes upon 
favorable variations ; and after a time, as the descendants of each 
of these individuals also tend to vary, a new species of plant or 
animal, fitted for that special place, will be gradually formed. 

1 This is not quite exact, for it has been found that in some animals at the time 
when the chromosomes are reduced in number, there are an even number in the 
female sex cells but an odd number in the male sex cells. When the male cells 
divide to reduce the number of chromosomes, some sperm cells receive an odd 
and some an even number of chromosomes. Therefore, after fertihzation, some 
eggs have an even and some an odd number of chromosomes. The fertilized egg 
cells with the odd number of chromosomes develop into male animals ; the cells 
with the even number of chromosomes become females. The sex-determining 
chromosome is known as the accessory chromosome and is found in some worms, 
many insects, myriapods, spiders, and some mammals. 



Artificial Selection. — Darwin reasoned that if nature seizes 
upon favorable variants, then man, by selecting the variations he 
wanted, could form new varieties of plants and animals much more 
quickly than nature. No one can doubt, when we compare the im- 
proved breeds of dogs 
with the original wild 
dog, or cultivated fruits 
like the apple and peach 
with their wild ances- 
tors, that man has done 
much in the way of im- 
proving domesticated 
plants and animals. 
But how has this been 
accomplished ? 

Every farmer knows 
that to produce good 
results he must first 

Improvement in corn by selection. At the left, 
the corn improved by selection frorai the original 
type at the right. 


14 IS 16 

have good seed or good stock. The plants or animals must come 
from sturdy parents. Then they must have favorable conditions 

in which to grow, or they 
will not produce. They 
must have care. On aban- 
doned farms the plants 
soon tend to revert or go 
back to wild conditions. 
And if we are to produce 
better plants and animals, 
we must continually select 
the best products for 
breeding as well as give 
them the best environ- 
ment possible. 

Two Kinds of Variations 
Occur. — Variations in na- 
ture appear to be of two 
large number of peas or 


/ 2 18 101 151 98 29 4 1 = 405 


8mm. 9mm. lOmm. Ilmm. IBmm. 13mm. 14mm. ISmm. 16mm. 
These columns represent the numbers of 
beans of the different sizes. For these 405 
beans, Quetlet's curve would be a curved line 
joining the tops of the columns. 

sorts. If we measure the size of a 

beans, we find that though most of them are of a certain size 



others will be a little larger or a little smaller, and a very few 
will be very large or very small. A graph can be made from the 
results, which shows an even curve, known as Quetlet's (ketlaz) 
Curve. The phenomenon represented by this curve is known as 
continuous variation and is seen universally in nature. 

Occasionally, however, sudden changes or discontinuous varia- 
tions occur. Such was the famous ancon ram which suddenly 
appeared in 1791 in Massachusetts. This ram had such short 
legs that it could not jump fences. Hornless cattle, albinos, and 
the famous beardless wheat found by Mr. 
Fultz are examples of such variations. 
These are called mutants or sports. The 
term mutant has of later years been as- 
sociated with the Dutch naturalist, Hugo 
de Vries. Very rarely, as he found, 
chance mutations appear which breed 
true. In the evening primrose, for ex- 
ample, he found eight different muta- 
tions. This means that new species in 
nature may arise suddenly, instead of by 
very slow degrees, as Darwin believed. 
It is easily seen that such a condition 
would be of immense value to breeders, 
as new plants and animals much unlike 
their parents might thus be formed and 
perpetuated. About 1910, a bean mutant appeared in the South 
which was adapted to life in the cotton belt. As a result, more 
than 6,000,000 acres of these beans were grown in 1917. Mutants 
have appeared in tobacco, barley, wheat, oats, tomatoes, and 
potatoes. One of the important parts of the work of the plant 
breeder is to discover, isolate, and breed useful mutations. 

Selective Planting. — By selective planting we mean choosing 
the best plants and planting their seeds with a view of improving the 
yield in some definite particulars. In doing this we must not neces- 
sarily select the most perfect fruits or grains, but must select seeds 
from the best plants. Experiments in corn selection at the Uni- 
versity of Illinois have shown that the oil content of the grain, the 
starch content, the position of the ear on the plant, and other 

Bearded wheat, and a 
beardless mutant. 

Yellow YY .Oreenyy 

Round RR Wrinkled rr 







yY yy 

Above are diagrams of two of Mendel's experiments 
with monohybrids. At the left the characters of yel- 
low color of seed ( F) and green color of seed {y) are 
carried by the gametes of the (P) parent generation ; 
at the right, smooth surface of seed {R) and wrinkled 
surface of seed (r) . In the next (Fi or first filial) genera- 
tion, flowers produced by the hybrid seed are mated 
^-ith flowers from hybrid seed of similar parentage. 
Explain characters of the F2 generation from text. 

The dihybrid carries two pairs of characters. Thus the plants of the Fi generation 
have received from the chromosomes of the parents both characters of color and char- 
acters of seed surface and are mated with each other. In the F2 generation all four of 
the characters appear or are segregated out in the proportion of 9-3-3-1. Arrange 
the characters as single pairs and place them above and at the side of a series of 
squares, combine them in the squares, and you can predict the proportions of the' 
F2 generation in a dihybrid mating. 



factors could be improved but nothing new has been produced. In 
selecting wheat, for example, we might breed for a number of 
different characters, such as more starch, or more protein in the 
grain, a larger yield per acre, ability to stand cold or drought or 
to resist plant disease. Each of these characters would have to 
be sought separately and could be obtained only after long and 
careful breeding. Selection of seed is most important ; but in 
order to produce new varieties of plants, another method is used, 
known as hybridizing. 

Hybridizing. — We have already seen that pollen from one 
flower may be carried to another of the same species and produce 
seeds. If pollen from 
one plant is placed on 
the pistil of another of 
an allied species or va- 
riety, fertilization may 
take place and new 
plants be eventually pro- 
duced from the seeds. 
This process is known as 
hybridizing, and the 
plants produced by this 
process known as hy- 
brids. This process is a 
most painstaking one, if worth-while results are to be obtained. 
The two plants to be crossed must be selected with great care, 
they must be carefully protected from possible self-pollination 
and the transfer of pollen must be so restricted that no pollen 
except the desired kind shall reach the pistil. After the transfer 
of pollen, the flower must be covered, to prevent any other than 
the desired pollen from reaching the pistil. 

Hybrids are extremely variable, and often are apparently unlike 
either parent plant. Most hybrids have to be perpetuated by 
means of some of the methods of vegetative propagation, as they 
rarely breed true and often do not produce seeds. 

Heredity and the Work of Gregor Mendel. — By far the most 
important discovery for the plant and animal breeder was made by 
Gregor Mendel, the abbot of a monastery at Brunn, in what is 

In artificial pollination parts of the flower 
(shaded) are cut away, leaving only the pistil. 
Pollen is carried on a brush to the stigma, and 
then the pistil is covered with a paper bag. 


now Czechoslovakia. About 1865, Mendel bred peas in his 
monastery garden and found that certain characters, such as 
color of seeds, color of flowers, smooth and wrinkled coats, and 
other characters, are inheritable. Then he began a long series 
of experiments in which he crossed or hybridized peas having some 
of these different characters. For example, he crossed tall plants 
with short ones, or smooth peas with wrinkled ones. The results 
of these crossings showed that these characters are always trans- 
mitted to the next generation as units, not as blendings of the two 
opposing characters. This was his first great discovery, the inherit- 
ance of unit characters. 

The Law of Dominance. — But Mendel found, in crossing peas, 
that the first generation of hybrids always showed a curious result. 
One character would appear, while its opposite would seemingly 
be lost. If, for example, smooth and wrinkled peas were crossed, 
the hybrids were all smooth. If tall and short pea plants were 
bred,- the hybrids were all tall, and similar results were obtained 
with the other pairs of characters with which he experimented. 
This gave rise to the statement that certain unit characters are 
dominant over others, which are called recessive characters. 

The Law of Segregation. — But these recessive characters were 
not really lost. If some of the hybrid smooth-coated peas are 
fertilized by others of the same kind and their seeds planted, the 
next generation (known to breeders as the F2 generation) will 
include some pea plants bearing smooth peas and some bearing 
wrinkled peas, in the ratio of 75 : 25. One quarter of all the peas 
show the recessive character. If these peas having the recessive 
character are crossed with each other in another generation, they 
will produce all wrinkled peas, the recessive character ; and such 
peas, when crossed again and again with peas of the same kind, 
will continue to produce wrinkled peas. The recessive character 
has been segregated out and is now known as an extracted recessive. 
This shows Mendel's Law of Segregation. Its importance in plant 
and animal breeding can readily be seen. 

The 75% of F2 peas which are seemingly all smooth-coated are 
in reality 25% smooth and 50% mixed, that is, having both char- 
actj5rs, the recessive hidden by the dominant. If we can separate 
the pure dominants^ they will produce only dominants, while the 



mixed hybrids will continue to breed dominants and recessives in 
the ratio of 25% dominant, 50% mixed, and 25% recessives. In 
crossing white Andalusian fowls with black ones, the hybrids are a 
bluish type (really white and black splashed feathers). The blue 
hybrids, if crossed, produce 25% black, 50% blue, and 25%, white. 
The whites will always breed whites, the blacks will breed black, 
while the blues, if crossed, will con- 
tinue to give the ratio of 25% black, 
50% blue, and 25% white. Here 
black is evidently a dominant and 
white a recessive character. The 
production of plants or animals 
having dominant and recessive 
character is based on the laws of 
chance. In hybrid peas (i^i, page 
386), for example, half the pollen 
grains would bear germ cells con- 
taining the determiner of ^'smooth" 
(R) and half the determiner of 
" wrinkled " (r), while in the ovule, 
half would contain the determiner 
''smooth'' and half ''wrinkled." 
Crossing them, we have in the F^ 
generation, the result shown on 
page 386. 

Dihybrids and Others. — Though 
breeding for one pair of characters 
is comparatively easy to under- 
stand, we often find breeders cross- 
ing for two or more pairs of characters. This is purely a matter 
of mathematics (on paper) as the diagram on page 386 shows, but 
it is too difficult to study in an elementary course in biology. At 
the present time most of the really valuable work in plant and 
animal breeding is being done by this method of Mendel. Not 
only does this enable breeders to fix the unstable hybrid char- 
acters, but also it enables them to combine worth-while characters 
such as immunity to diseases of various kinds, early ripening, 
color or size of fruit, and many other characters. 

H. NEW CIV. BIOL. — 26 

Law of segregation iHu^l^rated in 
three generations of rats. Here the 
gray color is a dominant character 
and the white is recessive. (Explain 
from the text.) 



The Practical Results. — Already some progress has been made 
in the application of Mendel's laws to hybridization. The United 
States Department of Agriculture is now producing cold-resistant 
fruits and grains in the Alaska experiment station. A hybrid which 
is a cross between the watermelon and the citron has produced a 
fruit that will resist " wilt/' a serious fungus disease of melons. 
Rust-resisting wheats also have been produced in this country; 
while in England experiments on wheat have resulted in the 
production of resistance to disease, " hardness " of grain, and in- 
crease in the size of the grain and of the head — all characters 
which mean greater productiveness. But most of the hybridizing 
is still done on a hit-or-miss principle, with few permanent results. 

General view of field plots devoted to experiments with cereals. View taken from 
Military Road at Arlington Experiment Farm, Arlington, Virginia. 

Luther Burbank, the great hybridizer of California, destroyed 
tens of thousands of plants in order to get one or two with the 
characters which he wished to preserve. A number of years ago 
he succeeded in producing a new variety of potato, which in a few 
years enriched the farmers of this country to the extent of millions 
of dollars every year. One of his varieties of black walnut trees, 
a very valuable hard wood, grows ten to twelve times as rapidly 
as ordinarj^ black walnuts. With lumber steadily increasing in 
price, a quick-growing tree becomes a very valuable commercial 
product. Among his famous hybrids are the plumcot, a cross 
between an apricot and a plum, numerous varieties of berries, and 
the splendid " Climax " plum, the result of a cross between a 
bitter Chinese plum and an edible Japanese plum. But practically 


none of Burbank's products grow from seeds; nearly all are 
propagated from hybrids by budding, grafting, layering, or slipping. 

The Department of Agriculture is also doing splendid work in 
producing new varieties of oranges and lemons, of grains and of 
various garden vegetables by use of hybridizing methods. 

Animal Breeding. — It has been pointed out that the domesti- 
cation of wild animals — horses, cattle, sheep, goats, and dogs — 
marked great advances in civilization in the history of mankind. 
As the young of these animals were bred in captivity, the people 
owning them would undoubtedly pick out the strongest and best 
of the offspring, killing the others for food. Thus man uncon- 
sciously aided nature in producing a stronger and a better stock. 
Later, he began to recognize certain characters that he wished 
to have in horses, dogs, or cattle, and by slow processes of breeding 
and of '' crossing " or hybridizing one nearly allied form with 
another, the numerous groups of domesticated animals began to 
be developed. 

Some Domesticated Animals. — Our domesticated dogs are 
descended from a number of wolflike forms in various parts of the 
world. All the present races of cats, on the other hand, seem to 
be traced back to Egypt. Modern horses are first noted in Europe 
and Asia, but far older forms flourished on the earth in earlier 
geologic periods. It is interesting to note that America was the 
original home of the horse, although at the time of the earliest 
explorers the horse was unknown here, the wild horse of the West- 
ern plains having descended from horses introduced by the 
Spaniards. The horse, which for some reason disappeared in this 
country, continued to exist in Europe, and man, emerging from his 
early savage condition, began to make use of the animal. We 
know the horse was domesticated in early Biblical times, and that 
it was one of man's most valued servants. In more recent times, 
man has begun to change the horse by breeding for certain desired 
characters. In this manner have been established and improved 
the various types of horses familiar to us as draft horses, coach 
horses, hackneys, hunters, and trotters. 

It is needless to say that all the various domesticated animals 
have been tremendously changed by breeding since they were 
brought under the control of civilized man. When we realize 


there were in 1925 nearly 19,000,000 horses, nearly 67,000,000 
cattle, over 40,000,000 sheep, and about 65,000,000 swine in this 
country, representing a money value of over $4,000,000,000, we 
see how very important a part the domestic animals play in our 

Present Problems in Animal Breeding. — In spite of the fact 
that this vast amount of money is represented by our domesticated 
animals, it could and should be much more. Crosses in fowls 
have been obtained that produce as many as 300 eggs from one 
hen in a year; yet the average hen lays less than 100 per year. 
A few cows of superior breeding in some of the state experiment 
stations produce as much as 1000 pounds of butter fat each in a 
year ; but the average cow produces little more than 200 pounds a 
year. A bulletin of the Department of Agriculture says, " Good 
judges believe that in the entire country one fourth of the cows 
kept for their milk do not pay for their cost of keeping, and nearly 
a fourth more fail to yield annual profit." This means that many 
farmers do not know what their cows are producing. It means that 
many farmers are poor, through either carelessness or ignorance. 
The scientific breeding of milk cows would mean millions of dollars 
in the pockets of the farmer, and an increase in that much-needed 
commodity, milk, for our children. This is only one of the many 
problems of conservation that will eventually be solved by our 
animal breeders. 

Summary. — Variation and heredity are always at work in 
living things. Man has made use of these tendencies for ages, 
once blindly, but now with some knowledge. Since the discovery 
of Mendel that unit characters are handed down by heredity, and 
that the inheritance of these characters can be determined exactly, 
our problems of plant and animal breeding have been made much 
more exact. Selection of strong animals and plants is necessary, 
conditions of culture must be carefully controlled, but the determi- 
nation and isolation of beneficial unit characters is the big problem 
for the future. 

Problem Questions 

1, What is heredity? How is it believed to be brought about ? 

2. What is variation? What two kinds of variations are there? Arej 
they of eaual value in breeding? 


3. What is artificial selection? Of what value is it? 

4. What are hybrids and how are they formed ? 

5. What are Mendel's Laws? Can you explain how segregation takes 

6. Give some examples of results of hybridization in plants and animals. 
Use the Journal of Heredity if possible for reference. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Alwood, A Civic and Economic Biology. P. Blakiston's Son and Company. 
Babcock and Clausen, Genetics in Relation to Agriculture. McGraw-Hill Book 

Downing, The Third and Fourth Generation. University of Chicago Press. 
Doncaster, The Determination of Sex. Cambridge University Press. 
Guyer, Being Well Born. The Bobbs-Merrill Company. 
Gruenburg, Biology and Human Life. Ginn and Company. 
Jewett, The Next Generation. Ginn and Company. 
Osterhout, Experiments with Plants. The MacmUlan Company. 
Harwood, New Creations in Plant Life. The Macmillan Company. 
Walter, Genetics. The Macmillan Company. 
Punnett, Mendelism. The Macmillan Company. 
Farmers' Bulletins: 195, 461, 576, 619, 887, 952, 1040, 1167, 1192, 1209, 1263, 

1332, 1369. 
Journal of Heredity, Numerous Articles. American Genetic Association, 



Problems : How did man become civilized f 

What is social inheritance ? 

What is the meaning of euthenics f 

What is the triangle of life ? 

What is the meaning of eugenics f 

Do Mendel's laws apply to man f 

How may we make use of this knowledge f 

Laboratory Suggestions 

Demonstration. The germ cells of ascaris or of a sea urchin, to show chromo- 

Home project. A study of the controllable factors of my environment. 

Home or laboratory study. To make a comparison of some applications of 
the laws of heredity. 

Home project. How may I determine my future vocation? 

Home project. To work out the inheritance of certain traits or peculiarities 
in my own family. 

How has Man become Civilized ? — It is a far cry from the 
home of the cave man to the elaborate structures in which we live 
to-day, and from his simple life to the rush and bustle of a modern 
city. Let us see how such progress has been achieved. 

We have seen that instinct plays an important part in the lives 
of animals lower than man. A baby chick just hatched pecks at 
a bad-tasting worm and receives a sense impression, so that after 
a few more mistakes of the same kind, it learns that such worms 
are not good and must be left alone. Man not only learns to 
profit by experience, as does the chick, but in addition he passes 
on this knowledge to others. While we cannot hand on this 
knowledge by heredity, we can teach others, and they in turn 
can teach their generation. In this way our race has made wonder- 
ful progress, the benefits of which we are now enjoying. This great 




mass of experience, which results in better health and such things 
as pianos, motor cars, and airplanes, is called our social inheritance. 

Euthenics and its Meaning. — People to-day have a chance to 
live longer than their ancestors because their environment is better. 
The sanitary conditions are much improved and disease germs are 
being controlled. We have found that if we wish to improve plants 
or animals, we must give them the best possible environmental 
conditions. So to-day science has taught us that if civilization is 
to progress, the race must have the best environment possible. 
Now laws are enforced to make for better housing conditions, our 
water and milk supplies are watched and protected against con- 
tamination, sewage is disposed of, streets are paved and cleaned. 
The lives of children have been so well protected that the average 
span of human life has been lengthened more than ten years since 
1875, owing largely to the application of scientific knowledge. 
Children are protected by law from the slavery that existed for 
some of them in factories and shops half a century or more ago. 
In the spring of 1913 the health department and street-cleaning 
department of the city of New 
York cooperated to bring about 
a " clean up " of all filth, dirt, 
and rubbish from the houses, 
streets, and vacant lots in that 
city. During the summer of 
1913 the health department 
reported a smaller percentage 
of deaths of babies than ever 
before. Similar experiments 
have been performed in other 
cities with similar results. 
We must draw our own con- 
clusions. The study of all the factors which make for a better 
environment is called Euthenics. 

The Triangle of Life. — A good many discussions have taken 
place on the question, ''Which is more important to a person, his 
environment or his heredity? " We now know that life is influ- 
enced by three great factors : training, or social heredity, environ- 
ment, or what we come in contact with, and heredity, or what we 

The triangle of life. 



are. All three play a part in shaping our destinies. It is self- 
evident that a handicap such as poor health or lack of education 
would play an important part in one's success or failure in life. 
Some men have become great in spite of handicaps, but it was 
because their heredity was such that they could not be denied 
success. Let us, then, see if the laws of heredity of which we 
learned in the last chapter can be applied to man. 

Chromosomes the Bearers of Heredity. — Investigations of 
heredity have centered, in late years, on the composition and action 

of the chromosomes, those tiny 
Yelloiv bod/ mm Cray body structures within the nucleus 

mite eye flfl ^^^^/^ of every cell. It has been 

found that they differ in num- 
ber according to the species of 
the animal. In a little worm 
called ascaris and in the fruit 
fly, there are only four chromo- 
somes in each germ cell; in 
the mosquito culex there are 
six, in the rat sixteen, in the 
frog twenty-four, in certain 
crustaceans more than one 
hundred and fifty, in one 
spider a hundred and sixty- 
eight. In some animals, as has been shown, the number differs 
with sex. Man is believed to have forty-eight. 

Professor Morgan of Columbia University has found, as a result 
of investigations on the fruit fly (drosophila) , that each chromo- 
some is actually composed of inheritable stuff that represents 
unit characters, and that some of these characters are linked to- 
gether in the same sex. This would explain some of the characters 
common to only male or female animals. 

It is plain that with forty-eight chromosomes, each of which is 
probably made up of a large number of determiners of unit char- 
acters, heredity in man is a very complicated matter at best. 
But a number of unit characters have been found which are in- 
heritable according to Mendel's laws, and undoubtedly others will 
be added as we learn more about the working of these laws. 

Normal mn§\ 

yermilion eye] 
Miniature mng 

Rudiiuenfary mni\ 
Forked bristles 
Complete eye 

Normal iving 

Red eye 


Hudimenfary tvin^ 
Forked bristles 
Bar eye 

Section through two chromosomes, show- 
ing how each may contain several separate 
unit characters. 


Characters Known to be Inheritable. — The following table 
indicates some of the characters in man that have been proved to 
be inheritable according to the laws of Mendel. 

Dominant Character 
Black or brown eye 
Pigmented iris 
Dark skin 
Curly hair 
Dark hair 

Congenital white lock 
Beaded hair 
Nervous temperament 

Recessive Character 
Blue or gray eye 
No pigment in iris 
Light skin 
Straight hair 
Light hair 
Normal hair 
Straight hair 
Phlegmatic temperament 

More study has been given to the inheritance of defects and 
susceptibility to diseases. Although these studies have been in 
progress only a few years, the following list probably is approxi- 
mately correct. 

Dominant Character 
Two- jointed fingers 
Extra digit 

Congenital cataract of eye 
Abnormally short limbs 
Hairless or toothless condition 
Spotted hair coat 
Huntington's chorea 

Recessive Character 
Normal fingers 
Normal number of digits 
Normal condition of eye 
Normal limbs 

Cases where the defect is recessive to the normal condition are 
much more difficult to find, but the following examples appear to 
be well established, according to Guyer : 

Dominant Character 
Normal pigment 
Normal intellect 
Normal intellect 


Recessive Character 

Albino skin 


Alcoholism (when based on feeble- 

Susceptibility to cancer 

Tendency to asthma or hay fever 

Probable susceptibility to tuberculosis 

Chorea (St. Vitus's dance) 

Lack of muscular control and several 
other less known diseases. 



Since our knowledge of heredity has been increased, the demand 
has become more urgent that we do something to prevent the race 
from handing down diseases and other defects, and that we apply 
to man some of the methods we employ in breeding plants and 
animals. This is not a new idea ; the Greeks in Sparta had it, 
Sir Thomas More wrote of it in his Utopia, and to-day it has been 
brought to us as the science of eugen'ics. The word comes from 
the Greek word eugenes, which means well born. Eugenics is the 
science of being well born, or born well, healthy, fit in every way. 
A tendency to cancer, or tuberculosis, or chorea, or feeble-minded- 
ness, is a handicap which it is not merely unfair, but criminal, to 
hand down to posterity. 

Two Notorious Families. — Studies have been made on a num- 
ber of different families in this country, in which mental and moral 
defects were present in one or both of the parents as far back as it 
was possible to trace the family. The ^' Jukes " family is a notori- 
ous example. " Margaret, the mother of criminals, is the first 
mother in the family of whom we have record." Up to 1915 there 



£S E hM 

This chart begins with a grandson of Margaret, " mother of criminals," and 
shows the character of some of his descendants. Squares represent males ; circles, 
females. A^", normal ; C, criminal ; Sx, immoral. 

were 2094 members of this family ; 1600 were feeble-minded oi 
epileptic, 310 were paupers, more than 300 were immoral womenj 
and 140 were criminals. The family has cost the state of New Yorl 
more than $2,500,000, besides immensely lowering the moral tone 
of the communities which the family contaminated. 

Another careful investigation (up to 1912) concerned the " Kal- 
likak " family. This family was traced to the union of Martii 
Kallikak, a young soldier of the War of the Revolution, with 


feeble-minded girl. She had a feeble-minded son, who had 480 
descendants. Of these 33 were sexually immoral, 24 confirmed 
drunkards, 3 epileptics, and 143 feeble-minded. The man who 
started this terrible line of immorality and feeble-mindedness 


Q-rlililEOQ 0®(^ 






in infancy 







Part of the two lines of descendants of Martin Kallikak. Squares represent 
males ; circles, females. A^, normal ; F, feeble-minded. 

later married a normal Quaker girl. From this couple a line of 496 
descendants was traced, with no cases of feeble-mindedness. The 
evidence and the moral speak for themselves ! 

Parasitism and its Cost to Society. — Hundreds of bad families 
such as those described exist to-day, spreading disease, immorality, 
and crime to all parts of this country. The cost to society of such 
families is very severe. Just as certain animals or plants become 
parasitic on other plants or animals, these families have become 
parasitic on society. They not only do harm to others by corrupt- 
ing, by stealing, and by spreading disease, but they are actually 
protected and cared for by the state out of public money. It is 
estimated that between 25% and 50% of all prisoners in penal in- 
stitutions are feeble-minded. Largely for them the poorhouse and 
the asylum exist. They take from society, but they give nothing 
in return. They are true parasites. 


The Remedy. — One unfortunate fact is that feeble-minded 
people have little sense of morality, for they have stopped short of 
normal mental development. Feeble-mindedness is a very serious 
problem, for it is estimated that at the lowest figure there are 
600,000 feeble-minded persons in this country, most of whom are 
free to breed their kind. The only real remedy seems to be to 
segregate the feeble-minded according to sexes in asylums and in 
various ways to prevent marriage and the possibilities of perpetu- 
ating such a low and degenerate race. Remedies of this sort have 
been tried successfully in Europe and are now meeting with suc- 
cess in this country. 

Blood Tells. — Eugenics shows us, on the other hand, in a study 
of families in which brilliant men and women are found, that 
the descendants have received the good inheritance from their 

The following, taken from Davenport's Heredity in Relation to Eugenics, 
illustrates how one family has been famous in American history. 

In 1667 Elizabeth Tuttle, " of strong will and of extreme intellectual vigor, 
married Richard Edwards of Hartford, Conn,, a man of high repute and great 
erudition. From their one son descended another son, Jonathan Edwards, 
a noted divine and president of Princeton College. Of the descendants of 
Jonathan Edwards much has been written; a brief catalogue must suffice: 
Jonathan Edwards, Jr., president of Union College; Timothy Dwight, presi- 
dent of Yale ; Sereno Edwards Dwight, president of Hamilton College ; Theo- 
dore Dwight Woolsey, for twenty-five years president of Yale College ; Sarah, 
wife of Tapping Reeve, founder of Litchfield Law School, herself no mean lawyer ; 
Daniel Tyler, a general in the Civil War and founder of the iron industries 
of North Alabama; Timothy Dwight, second, president of Yale Univer- 
sity from 1886 to 1898; Theodore William Dwight, founder and for thirty- 
three years warden of Columbia Law School ; Henrietta Frances, wife of Eli 
Whitney, inventor of the cotton gin, who, burning the midnight oil by the side 
of her ingenious husband, helped him to his enduring fame ; Merrill Edwards 
Gates, president of Amherst College ; Catherine Maria Sedgwick, of graceful 
pen; Charles Sedgwick Minot, authority on biology and embryology in the 
Harvard Medical School ; Edith Kermit Carow, wife of Theodore Roosevelt ; 
and Winston Churchill, the author of Coniston and other well-known novels." 

The daughters of Elizabeth Tuttle had distinguished descendants. Robert 
Treat Paine, signer of the Declaration of Independence ; Chief Justice of the 
United States Morrison R. Waite; Ulysses S. Grant and Grover Cleveland, 
presidents of the United States. These and many other prominent men and 
women can trace the characters which enabled them to occupy the positions 
of culture and learning they held back to Elizabeth Tuttle. 



Traits that are Inherited. — Many other similar cases might be 
cited. Although we do not know the precise method of inherit- 
ance, we do know that musical and literary ability, calculating 
ability, remarkable memory, mechanical skill, and many other 
mental and physical characters are inheritable and '^ run in fami- 
lies." The Wedge wood family, from which three generations of 
Darwins have descended, and the Galton family are examples of 
a scientific inheritance ; the Arnolds, Hallams, and Lowells were, 
prominent in literature ; the Balf ours were political leaders ; the 

[i]t# HtO 

A record of good inheritance. Black squares represent men of artistic ability ; 
black circles, women of artistic ability. (After Davenport.) 

Bach and Mendelssohn familes were examples showing inheritance 
of musical genius. A comparison of fathers' and sons' college 
records at Oxtord University show it is usually " like father, like 
son " as regards grades. The fathers who did well had sons who 
did well also. It is said that 26 out of 46 men chosen to the Hall 
of Fame of New York University had distinguished relatives. 
Blood does tell ! 

How to use Our Knowledge of Heredity. — Two applications of 
this knowledge of heredity stand out for us as high school students. 
One is in the choice of a mate, the other in the choice of a vocation. 
As to the first, no better advice can be given than the old adage, 
" Look before you leap." If this advice were followed, there 
would be fewer unhappy marriages and divorces. Remember that 
marriage should mean love, respect, and companionship for life. 
The heredity of a husband or a wife counts for much in making 
this possible. And, even though you are in high school, it is 
only fair to yourselves that you should remember the responsibility 
that marriage brings. You should be parents. Will you choose 
to have children well born ? Or will you send them into the world 
with an inheritance that will handicap them for life ? 


Choosing a Vocation. — The nearer problem for most of us is, 
*' What am I going to do after I leave high school? Will it be 
college and a profession? Or am I better fitted for a trade or 
business? I cannot afford to be a ' square peg in a round hole.' '* 
Some things are obvious. If you have inherited colorblindness, 
you could not become a locomotive engineer. The musical pro- 
fession would not be chosen by any one who had no musical sense. 
If our heredity is composed of physical and mental traits or char- 
acteristics, then there must be certain kinds of characteristics 
that fit us for success along certain lines of work. 

Self-Analysis Necessary ; Habits of Life. — To choose one's 
life work wisely, one must first analyze one's abilities and habits, 
both of which are very important. Do we have good posture? 
Are we neat in person and dress ? Do we dress quietly and in good 
taste? Do we cultivate smiles instead of ^' grouches "? Are we 
courteous ? Do we have good table manners ? Do we know how 
to use our speaking voice? Impressions made on employers are 
largely based on an estimate of such habits. Much of our life 
we control, and the formation of habits of industry, alertness, 
promptness, thoroughness, orderliness, tolerance, honesty, re- 
liability, and open-mindedness will go far in making for success in 

Abilities. — Certain natural abilities, tendencies, and instincts 
dependent on physical and mental heredity, must be considered 
also in choosing a vocation. Health is first of all. Certain kinds 
of work — mining, farming, forestry, stock raising, and many 
trades — demand a good constitution, if one is to ^' make good." 
Persons who become leaders in commercial life must have execu- 
tive power, system, energy, resourcefulness, and capacity to form 
sound judgments. Professional life makes demands upon muscles 
and brain in still another way. Let us examine a few cases to 
see just what is meant. 

Abilities Needed for the Professions. — For the ministry high 
ideals, faith, sympathy, power in thought and in word, capacity for 
sacrifice, conabined with knowledge acquired from books and 
people, are essentials. For the medical profession, certain skill of 
hand and eye which aids in making a delicate dissection, nerve, 
good eye-sight, ability to search for causes and to draw conclu- 


sions, together with sympathy, character, and love for the work, 
are essential to success. For engineering, mathematical and con- 
structive abilities are outstanding ; while a lawyer needs high rea- 
soning powers and ability to deal with men. The teacher should 
be well educated and, in addition, must love boys and girls. 
Health, tact, good nature, imagination, inventiveness, and enthu- 
siasm are some of the qualities which make the successful teacher. 

Abilities Needed in Commercial Life. — For all commercial 
life reliability, promptness, energy, cheerfulness, and high moral 
character are the basis. Stenographers and clerks need, in addi- 
tion, special skills, which will be increased in practice. If one is 
to become a manager or a promoter of a business, organizing and 
executive ability, good judgment, caution, and a knowledge of 
business affairs are necessary. The business man or woman 
should know people and have what we call '^ business sense " for 

Abilities necessary for Trades. — For the mechanical lines, 
knowledge of the trade is an essential, with skill of eye and of hand. 
Accuracy and loyalty are essentials, if one is to rise. For in- 
dustries of a semi-professional nature, such as illustrating, cartoon 
drawing, or engraving, the artistic abilities should be trained, and 
imagination, inventiveness, and appreciation of what the public 
want should be joined with the purely mechanical abilities which 
have to do with drawing or color work.^ 

Summary. — We have found that life is made up of our social 
inheritance or what we learn through our environment, but that 
success, after all, depends on our inheritance. Great men have 
attained success often in spite of handicaps of environment or of 
physical ailment. But no one becomes great unless he or she has a 
nervous system of a superior capacity. The most important 
things to be learned in this chapter are, first, to choose wisely 
when we select our mates, and second, to make a wise selection of 
our life work. These two decisions mean either future happiness 
or future woe. After making a choice we should bend all our 
energies and strive faithfully to attain success and happiness along 
the chosen path. 

^ For further information as to the conditions necessary to become efficient in 
any line of work, read Parsons, Choosing a Vocation, Hougl.ton Mifflin Company. 



Problem Questions 

1. What is social inheritance? How has it played a part in civilization? 

2. Give some examples of practical euthenics in your communit3^ 

3. How does the " triangle of life " play a part in your future ? 

4. What proofs are there that certain determiners of unit characters are 
handed down in the chromosomes? 

5. List the physical characters known to be inheritable by Mendel's 
Laws and see if you can account for the appearance of any of them in your 

6. What diseases are inherited in families ? Do you find any evidences of 
such diseases in your community? 

7. Show how the science of eugenics should deal with a family like the 
" Jukes " or " Kallikaks." 

8. What evidence have we that " blood will tell " in the heredity of genius ? 

9. In what ways can you personally make use of this chapter ? 

10. Would inherited characters play any part in choosing a vocation? 

11. Would habits play any part in making good in life? Explain. 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Allen, Civics and Health. Ginn and Company. 

Coulter, Castle, East, Tower, and Davenport, Heredity and Eugenics. Univer- 
sity of Chicago Press. 

Davenport, Heredity in Relation to Eugenics. Henry Holt and Company. 

Goddard, The Kallikak Family. The Macmillan Company, 

Jordan, The Heredity of Richard Roe. American Unitarian Association. 

KeUicott, The Social Direction of Human Evolution. D, Appleton and Com- 

Morgan, The Chromosome Theory of Heredity. Lippincott Company. 

Parsons, Choosing a Vocation. Houghton Mifflin Company. 

Punnet, Mendelism. The Macmillan Compan5^ 

Richards, Ellen M. Euthenics, the Science of Controllable Environment. 
Whitcomb and Barrows. 

Walter, Genetics. The Macmillan Company. 


If we were to attempt to group the men associated with the 
study of biology, we should find that in a general way they are 
connected either with discoveries of a purely scientific nature or 
with the improvement of man's condition by the application of the 
purely scientific discoveries. The first group is necessary in order 
that the second group may use the results. It was necessary for 
men like Charles Darwin and Gregor Mendel to advance their 
theories before Luther Burbank or any of the men now working in 
the Department of Agriculture could benefit mankind by produc- 
ing new varieties of plants. The discovery of scientific truths 
must be made before the men of modern medicine can apply them 
to the cure or prevention of disease. Since we are most interested 
in discoveries which touch directly upon human life, the men of 
whom this chapter treats will be those who, directly or indirectly, 
have benefited mankind. 

The Discoverers of Living Matter. — The names of a number of 
men living at different periods are associated with our first knowl- 
edge of cells. About the middle of the seventeenth century micro- 
scopes came into use. Through their use plant cells were first 
described and pictured as hollow boxes or " cells." But it was 
not until 1838 that two German friends, Schleiden (shlf den) and 
Schwann (shvan), working on plants and animals, discovered that 
both of these forms of life are built up of units called cells. 
Other biologists gave the name protoplasm to all living matter, and 
a little later Professor Huxley, a famous Englishman, friend and 
champion of Charles Darwin, called attention to the physical 
and chemical qualities of protoplasm so that it came to be known 
as the chemical and physical basis of life. 
d.. NEW crv. BIOL. — 27 405 


Life comes from Life. — Another group of men, after years of 
patient experimentation, worked out the fact that life comes from 
life. In ancient times it was thought that hfe arose sponta- 
neously; for example, that fish or frogs grew out of the mud of the 
river bottoms, and that insects came from dew or the rotting of 
meat. But Redi (ra'de), who Hved 1621-1697, proved by a sim- 
ple experiment that flies laid their eggs in rotting meat, and thus 
accounted for the maggots found there. It was believed that 
bacteria arose spontaneously in water, even as late as 1876, whei. 
Professor Tyndall proved by experiment the contrary to be true. 

In 1651 William Harvey, the court physician of Charles I of Eng- 
land, showed that Uving things came from egg cells. It was much 
later, however, that the part played by sperm and egg cell in 
fertilization was carefully worked out. It is to Harvey, too, that 
we owe the discovery of the circulation of the blood. He showed 
that blood moves in a complete circulation in the body and that 
the heart pumps it. Up to his time the arteries had been thought 
to be air tubes, because after death they were empty of blood. 
He might be called the father of modern physiology as well as of 

Van Leeuwenhoek (page 44), who lived 1632-1723, is remem- 
bered as the maker of an improved microscope, although his 
simple lenses were far from equaling our modern instruments. We 
also connect his name with Harvey's work, for it was he who first 
saw the circulation of blood in the capillaries. He says in speak- 
ing of circulation in a tadpole's tail, that '' Thus it appears that 
an artery and a vein are one and the same vessel, prolonged and 

A long list of other names might be added to show how gradually 
our knowledge of the working of the human body has been in- 
creased. At the present time we are far from knowing all the func- 
tions of the various parts of the human engine, as is shown by the 
number of investigators in physiology at the present time. Pres- 
ent-day problems have much to do with the care of the human 
mechanism and with its surroundings. The solution of these 
problems will come from the application of hygiene, preventive 
medicine, and sanitation. 

In the preceding chapters of this book we have learned some- 



thing about our bodies and their care. We have found that man 
is able within hmitations to control his environment so as to make 
it better to live in. All of the scientific facts that have been of 
use to man in the control of diseases have been found out by men 
who have devoted their lives to their work in the hope that their 
experiments and their sacrifices of time, energy, and sometimes of 
life itself might make for the betterment of the human race. Such 
men were Jenner, Lister, Koch, 
and Pasteur. 

Edward Jenner and Vacci- 
nation. — The civilized world 
owes much to Edward Jenner, 
the discoverer of vaccination 
to prevent smallpox. Born in 
Berkeley, a little town of 
Gloucestershire, England, in 
1749, as a boy he showed a 
strong liking for natural his- 
tory. He studied medicine and 
also gave much time to the 
working out of biological prob- 
lems. As early as 1775 he 
began to associate the disease 

called COWpOX with that of Edward Jenner. 

smallpox, and gradually the idea of inoculation to prevent this ter- 
rible scourge, which killed or disfigured hundreds of thousands every 
year in England alone, was worked out and applied. He believed 
that if the two diseases were similar, a person inoculated with the 
mild disease (cowpox) would after a slight attack of this disease 
be immune to the more deadly and loathsome smallpox. It was 
not until 1796 that he was able to prove his theory, as at first few 
people would submit to vaccination. War at this time was being 
waged between France and England, so that the former country, 
usually quick to appreciate the value of scientific discoveries, was 
slow to give this method a trial. In spite of much opposition, how- 
ever, by the year 1802 vaccination was practiced in most of the civ- 
ilized countries of the world. At the present time the death rate 
from smallpox in Great Britain, the home of vaccination, is less than 


.3 to every 1,000,000 living persons. This shows that the disease is 
practically v/iped out in England. An interesting comparison 
might be made between these figures and those showing the 
occurrence of the disease in parts of Russia where vaccination is not 
practiced. There, thousands of deaths from smallpox occur an- 
nually. During the winter of 1913-1914 an epidemic of smallpox 
with more than 250 cases broke out in the city of Niagara Falls. 
This epidemic appears to have been the result of a campaign con- 
ducted previously by people who did not believe in vaccination. 
In cities and towns near by, where vaccination was practiced, no 
cases of smallpox occurred. During the year 1925 there were 
more than 9000 cases of smallpox in California ; and these cases 
were not centered among the Mexicans and other foreigners but 
largely among young people of school age whose parents did not 
believe in vaccination. Since some stubborn opposition to vac- 
cination is found nowadays, Jenner naturally had a much harder 
battle in his day. He also had many failures, due to the imperfect 
methods of his time. The full worth of his discovery was not ap- 
preciated until long after his death, which occurred in 1823. 

Louis Pasteur. — The man who, from a biological point of view, 
did more than any other to benefit mankind directly was Louis 
Pasteur. Born in 1822, in the mountains near the border of north- 
eastern France, he spent the early part of his life as a normal coun- 
try boy, fond of fishing and not very partial to study. He inherited 
from his father, however, a fine character and a grim determination, 
so that when he became interested in scientific pursuits he settled 
down to work with enthusiasm and energy. 

At the age of twenty-five he became well known throughout 
France as a chemist. Shortly after this he became interested in 
bacteria, and it was in the field of bacteriology that he became most 
famous. First as professor at Strasbourg, then at Lille, and later 
as director of scientific studies in the Ecole Normale at Paris, he 
showed his interest in the application of his discoveries to human 

In 1857 Pasteur showed that bacteria are connected with the 
process of fermentation, and that it is not a purely chemical 
process as had been thought up to that time. This discovery 
led to very practical ends, for France was a great wine-producing 



country, and with a knowledge of the cause of fermentation it was 
possible to check the diseases which had spoiled wine. 

In 1865-1868 Pasteur turned his attention to a silkworm dis- 
ease which threatened to wipe out the silk industry of France and 
Italy. He found that this disease was caused by two tiny organ- 
isms, one a protozoan, the other a bacterium. After careful study 
he made certain recommendations which, when carried out, re- 
sulted in the complete conquest 
of the disease and the saving of 
millions of dollars to the poor 
people of France and Italy. 

His greatest service to man- 
kind came later in his life when 
he applied certain of his dis- 
coveries to the treatment of 
disease in people. First ex- 
perimenting upon chickens, he 
proved that a vaccine made 
from the germs which caused 
chicken cholera could be re- 
duced to any desired strength. 
He then inoculated chickens 
with the vaccine of reduced 
strength, giving them a mild 
form of the disease, and found 
that this made them immune. 
This discovery, first applied to 
chicken cholera, laid the foundation for all future work in the uses 
of serums, vaccines, and antitoxins. 

Pasteur is perhaps best known through his study of rabies. 
The great Pasteur Institute, founded by popular subscriptions 
from all over the world, has successfully treated many thousands 
of cases of rabies with a death rate of less than 1 per cent. But 
more than that, it was the place where Roux (roo), a fellow worker 
with Pasteur, discovered the antitoxin for diphtheria which has 
saved thousands of human lives. There also were estabhshed the 
principles of inoculation against bubonic plague, lockjaw, and other 
germ diseases. 

Louis Pasteur. 



Pasteur died in 1895 at the age of seventy-three, beloved by 
his countrymen and honored by the entire world. 

Robert Koch. — Another name associated with the battle 
against disease germs is that of Robert Koch (k6K). Born in 
Germany, in 1843, he later became a practicing physician, and 
about 1880 was called to Berlin to become a member of the sani- 
tary commission and professor 
in the school of medicine. In 
1881 he discovered the germ 
that causes tuberculosis and 
two years later the germ that 
causes Asiatic cholera. His 
later work was directed toward 
the discovery of a cure for 
tuberculosis and for other germ 
diseases. He died in 1910. 

Lister and Antiseptic Treat- 
ment of Wounds. — A third 
great benefactor of mankind 
was Sir Joseph Lister, an 
Englishman who lived 1827- 
1912. As a professor of sur- 
gery he first used antiseptics in 
the operating room. By means 
of the use of carbolic acid and 
other antiseptics on the surface 
of wounds, on instruments, and 
on the hands and clothing of the operating surgeons, germs were 
prevented from infecting the wounds. This single discovery has 
done more to prevent death after operations than any other of 
recent time. 

Modern "Workers on the Blood. — At the present time several 
names stand out among investigators of the blood. Paul Ehrlich 
(ar'liK), a German born in 1854, is justly famous for his work on 
the blood and its relation to immunity from certain diseases. His 
able research work has given the world a much better understand- 
ing of acquired immunity and has enabled physicians to fight the 
dread venereal disease, syphilis, with good results. 

Robert Koch. 



Another name associated with the blood is that of Elias Metch- 
nikoff, a Russian born in 1845. He first advanced the belief that 
colorless blood corpuscles, or phagocytes, do service as the sanitary 
police of the body. He has found that there are several different 
kinds of colorless corpuscles, each having different work to do. 
Much of the more modern work done on the blood is founded 
directly on the discoveries of Metchnikoff . 

Scores of other names also should be remembered. Walter 
Reed, the leader of the fight 
against yellow fever; Major 
Ross, who discovered the ma- 
larial parasite ; Carrell, who 
was responsible for the Carrell- 
Daiken treatment of wounds 
during the war ; Noguchi, the 
Japanese who made antitoxins 
against snake venom and yel- 
low fever ; Flexner, for his dis- 
coveries in connection with 
infantile paralysis ; the Dicks, 
husband and wife, who are 
working on a method of treat- 
ment for scarlet fever; and 
many others. 

Charles Darwin. — Another 
important line of biological 
investigation is the study of 
heredity and of the develop- 
ment of life on the earth. The name of Darwin is most indelibly 
associated with this branch of biology. 

Charles Darwin was born on February 12, 1809, a son of well- 
to-do parents, in the pretty English village of Shrewsbury. As a 
boy he was very fond of out-of-door life, was a collector of birds* 
eggs, stamps, coins, shells, and minerals. He was sent to Edin- 
burgh University to study medicine, but the dull lectures, coupled 
with his intense dislike for operations, made him determine never to 
become a physician. Instead, he was greatly interested in natural 
history, and in the proceedings of a student zoological society. 

Charles Darwin. 


In 1828 his father sent him to Cambridge to study for the 
ministry. His three years at this university were wasted so far 
as preparation for the ministry was concerned, but they were in- 
valuable in shaping his future. He made the acquaintance of one 
or two professors who were naturalists like himself, and in their 
company he spent many happy hours roaming over the coun- 
tryside collecting beetles and other insects. In 1831 an event 
occurred which changed his career and helped him to become one 
of the world's greatest naturalists. He received word through 
one of his friends that the position of naturalist on the ship 
Beagle was open for a trip around the world. Darwin applied for 
the position, was accepted, and shortly after started on an eventful 
five years' trip around the world. He returned to England a 
famous naturalist and spent the remainder of his long and busy 
life producing books which have done much to account for the 
changes of form and habits of plants and animals on the earth. 
His theories established also a foundation upon which plant and 
animal breeders were able to work. Two of his best known books 
are Origin of Species Sind Plants and Animals under Domestication. 
We have seen some account of his work on pollination (page 36) 
and his theory of " natural selection " (page 383). 

His interpretation of the ways in which all life changes and de- 
velops was due not only to his information and experimental evi- 
dence, but also to an iron determination and undaunted energy. 
In spite of almost constant illness brought about by eyestrain, he 
accomplished more than most well men have done. He died on 
the 19th of April, 1882, at seventy-four years of age. 

Other Scientists. — Thomas Henry Huxley did much to make 
people understand Darwin's work, as he was a wonderful teacher 
and lecturer. Associated with Darwin's name we must place also 
the names of two other co-workers on heredity, Alfred Russel 
Wallace, an Englishman who, working independently and at about 
the same time, reached many conclusions similar to those of Dar- 
win, and August Weissman, a German. The latter showed that 
the protoplasm of the germ cells (eggs and sperms) is handed 
down directly from generation to generation, these cells being dif- 
ferent from the others in the body from the very beginning of the 
development of the embryo. 



In 1883 a German named Boveri discovered that the chromo- 
somes of the egg cell and of the sperm cell are at the time of ferti- 
lization just half the number of those of the other cells (see page 
383), so that Si fertilized egg is really a whole cell made up of two 
half cells, one from each parent. The chromosomes, we remem- 
ber, are believed to be the bearers of the hereditary qualities 
handed down from parent to child. 

Applications to Plant and 
Animal Breeding. — Turning to 
the practical applications of 
the scientific work on the 
method of heredity, the name 
of Gregor Mendel, an Austrian 
monk, stands out most prom- 
inently. Mendel was born in 
1822. He early entered the 
Monastery at Brunn, where he 
lived until his death in 1884. 
In 1865 after several years of 
experimentation he published 
the results of his work on in- 
heritance in peas. But his work 
created no interest at the time 
and remained undiscovered 
until the year 1900, when it 
became world-famous. The 
application of his methods to 
plant and animal raising are 
of the utmost importance in 
assisting the breeder to develop the qualities he desires and breed 
for those qualities only. Another name often mentioned with 
reference to plant breeding is that of Hugo de Vries, the Dutch- 
man who recently showed that in some cases new kinds of plants 
arise by sudden and great variations known as mutations. Thomas 
Hunt Morgan, a professor at Columbia University, has actually 
produced new species of fruit flies as a result of his careful study 
of mutants. His work, with that of scores of other workers in 
heredity, is paving the way for the practical plant and animal 

Monument to Mendel at Brunn, 
Czechoslovakia. The inscription in Ger- 
man reads : "To the naturalist P. Gregor 
Mendel, 1822-1884. Erected 1910 by 
friends of science." 


breeders. And lastly, in California, Luther Burbank, by careful 
selecting and hybridizing, won lasting fame with his new and 
useful plant hybrids. 

Project References 

Conn, Biology. Silver, Burdett and Company. 

Darwin, Life and Letters of Charles Darwin. D. Appleton and Company. 
Locy, Biology and Its Makers. Henry Holt and Company. 
Locy, Main Currents of Zoology. Henry Holt and Company. 
Pminett, Mendelism. The Macmillan Company. 
Thompson, Heredity. John Murraj^, London, England. 
Vallery-Radot, The Life of Pasteur. Doubleday, Page and Company. 
Caldwell and Slosson, Science Remaking the World. Doubleday, Page and 


(Generic and specific names are not included. For names of phyla, classes, 
and orders, see pages 235 to 249.) 


Abdo'men (Lat. abdomen, belly) : the posterior region of the body of an insect ; 

the region of the body below the chest in man. 
Absorp'tion (Lat. absorber e, to swallow down) : the process of taking up liquid 

food or other substances through the walls of cells. 
Adapta'tion (Lat. adaptare, to fit) : fitness for surroundings ; fitness to do a 

certain kind of work ; changes which a plant or an animal has undergone 

that fit it for the conditions in which it lives. 
Ad'enoids : fleshy growths in the back of the nose cavity which clog the air 

Adult' : grown to full size and maturity. 

Adul'terant : a substance put in another to cheapen it ; usually reducing its 

' strength or otherwise injuring it. 
Aero'bic organisms : bacteria or other organisms which require free oxygen, 

as opposed to anaerobic organisms (bacteria and some parasitic worms) 

which do not require free oxygen. 
Agglu'tinins (Lat. agglutinare, to glue to) : antibodies found in blood which 

cause bacteria to be clumped together, preparatory to their destruction 

by the colorless corpuscles. 
Albu'min : a protein forming an important part of the blood and found also 

in many animal and vegetable substances. 
Alimen'tary canal (Lat. alimentum, food) : the food tube. 
Altema'tion of generations : the alternating of a sexual with an asexual genera- 
tion in the life-history of a plant or an animal. 
Am'ino-acid : a fragment of a complex protein ; one of the simpler substances 

into which a protein may be broken down in the body. 
Anal'Dgy : likeness in function. 
Anten'na (pi. Antennae) (Lat. antenna, a sailyard) : a jointed feeler on the 

head of an insect or of a crustacean. 
Ante'rior (Lat. anterior, former) : nearer the head end (Zool.) ; facing outward 

from the axis (Bot.). 
An'ther (Gr. antheros, flowery) : the part of the stamen which develops and 

contains pollen. 
An'tibodies : substances found in the blood which fight against bacteria or 

prevent them from harming the body. 



Antisep'tic (Gr. anti, against ; sepsis, putrefaction) : a substance which prevents 

the growth of harmful microorganisms. 
Antitox'in : a substance that neutraUzes a toxin. 
A'nus (Lat.) : the posterior opening of the food tube. 

Aor'ta (Gr. aorte, from aeirein, to Hft) : the large artery leaving the left ventri- 
cle of the heart. 
Append'age : a jointed organ attached to the side of the body. 
Ar'tery (Lat. arteria, windpipe, artery) : a tube which conveys blood from the 

Asep'tic (Gr. a, not ; septikos, putrid) : free from pus-forming bacteria or other 

harmful organisms. 
Asex'ual : having no sex. 
Assimila'tion (Lat. assimilare, to make like) : the converting of digested food 

into living matter. 
Astig'matism (Gr. a, without ; stigma, spot) : a defect of the eye, caused by 

an irregularity in the curvature of the lens. It results in indistinctness 

of vision. 
Au'ricle (Lat. auricula, little ear) : a chamber in the heart which receives 

Autonom'ic nervous system (Gr. autos, self ; nomos, province) : a part of the 

nervous system not under control of the will ; the sympathetic nervous 

Ax'on : the main elongation of a neuron. 


Bacillus : a rod-shaped bacterium. 

Bacte'ria (Gr. hakterion, a little staff) : microscopic one-celled plants, some of 
which cause specific diseases. 

Bacteriorogy : a study of bacteria. 

Bast : tough, fiberlike cells composing the inner layer of bark. 

Bile : a fluid secreted by the liver. 

Biorogy (Gr. hios, life ; logos, word or discourse) : the study of matter in a liv- 
ing state ; the study of plants and animals. 

Blade : the flat portion of a leaf. 

Blas'tula (Gr. blastos, a bud) : a stage in the segmentation of an egg in which 
the cells form a hollow ball with a wall one layer thick. 

Bud : an undeveloped branch. 

Cal'orie (Lat. calere, to be warm) : a heat unit, namely, the amount of heat 
required to raise the temperature of one kilogram of water one degree 
Centigrade. (See note on page 119.) 

Calorim'eter : a machine for measuring heat. 

Cam'bium : the growing layer of a dicotyledonous stem. 


Cap'illaries (Lat. capillus, a hair) : minute tubes which connect arteries with 

Capillar'ity : a phenomenon shown by hquids rising in fine tubes. 
Carbohy'drate (Lat. carbo, coal ; Gr. hydor, water) : a class of nutrients com- 
posed of carbon, oxygen, and hydrogen, having the oxygen and hydrogen 

in the same proportion as water. 
Car'bon (Lat. carbo, coal) : an element found in all organic compounds. 
Carbon dioxide : a gas, a product of the oxidation of carbon. 
Cell : the structural and physiological unit in plant and animal bodies. A 

small mass of protoplasm in most cases inclosed in a cell membrane and 

usually containing a nucleus. 
Cell membrane : the delicate living covering of a cell. 

Cell sap : water, with materials in solution, found in the vacuoles of plant cells. 
Ceriulose ': a dead substance found in the walls of plant cells. 
Cerebellum (Lat., diminutive of cerebrum) : part of the brain between the 

cerebrum and the medulla oblongata. 
Cer'ebnim (Lat. cerebrum, the brain) : the anterior part of the brain. 
Chemical compound : a substance formed by the combination of chemical 

Chemical element : a simple substance ; one which cannot be formed by the 

combination of simpler substances. 
Chi'tin (Gr. chiton, a tunic) : a hard, nitrogenous substance present in the exo 

skeleton of insects. 
Chlo'rophyll (Gr. chloros, grass green ; phyllon, a leaf) : the green coloring 

matter of plants. 
Chlo'roplasts : small bodies of protoplasm which contain chlorophyll. 
Cho'roid : the middle coat of the eye. 
Chro'mosome (Gr. chroma, color ; soma, body) : a deeply staining body in the 

nucleus of a cell, supposed to carry the determiners of hereditary qualities. 
Chrys'alis (Gr. chrysos, gold) : the uncovered pupal stage of butterflies. 
Cil'ium (Lat. cilium, an eyelid with hairs growing on it) : a tiny hairlike thread 

of protoplasm extending from a cell. 
Cloa'ca (Lat. cloaca, sewer) : the common cavity into which the digestive, 

urinary, and reproductive systems open in some kinds of vertebrates. 
Coc'cus (Gr. kokkus, berry) : a ball-shaped bacterium. 
Cocoon' : a silky covering around a pupa ; the egg-case of spiders. 
Commu'nicable disease : a disease that can be passed directly from one person 

to another. 
Compound eye : an eye made up of many simple eyes or ommatidia. Arthro- 
pods have compound eyes. 
Conjuga'tion (Lat. cum, together with ; jugare, to yoke) : the temporary 

union of two sex cells of equal size, with a fusion of nuclei and interchange 

of nuclear material. 
Connective tissue : collections of cells which support and connect other tissues. 
Contrac'tile vac'uole : a small vesicle, found in the cytoplasm of many proto- 


zoa, which appears and disappears with regularity. It is beUeved to be 
an organ of excretion. 

Corol'la (Lat. corolla, a little crown) : the petals of a flower taken together. 

Cor'puscles (Lat. corpusculum, a little body) : the red enucleated cells and 
the colorless cells in the blood. 

Cor'tex : a fleshy portion of the root, outside the central cylinder. 

Cotyle'don (Gr. kotyledon, socket) : leaf of an embryo, in a seed. 

Cul'ture : a growth of bacteria or other microorganisms in a prepared nu- 
trient medium. 

Cy'toplasm (Gr. kytos, a vessel ; plasma, anything formed) : the living sub- 
stance of the cell outside of the nucleus and inside the cell membrane. 

Den'drites (Gr. dendron, tree) : delicate protoplasmic branched endings of a 

Der'mis (Gr. derma, skin) : the layer of skin below the epidermis. 

Di'aphragm (Gr. diaphragma, a partition wall) : the muscular partition be- 
tween the thorax aiid the abdomen. 

Di'astase : an enzyme formed in plants which changes starch to grape sugar. 

Dicotyle'don : a plant that bears seeds having two cotyledons. 

Dififu'sion : the passage of particles of a substance, either gas or liquid, from a 
point of greater to a point of lesser concentration. 

Diges'tion (Lat. digestio, the dissolving of food) : the process of preparing 
food for absorption. 

Dihy'brid. Mendelian term for a cross between organisms which differ in 
two pairs of alternative characters. 

Disease' : a state in which part of the body does not function properly. 

Disinfect'ant : something which kills bacteria. 

Dor'sal (Lat. dorsum, the back) : of or pertaining to the back or top side. 

Ductless glands : glands which have no communication with an outer surface, 
and which manufacture hormones. 


Ec'todenn (Gr. ectos, outside ; derma, skin) : the outer layer of cells in an 

Em'bryo (Gr. emhryon, a young one) : the early stage of a developing plant or 

Em'bryo sac : the structure within the ovule which holds the egg cell. 
Emul'sion (Lat. emulaere, to milk out) : a mixture of liquids which do not 

dissolve, the particles of one floating as small globules in the other. 
Enam'el : hardest part of a tooth. 

Encysf : to become inclosed in an impermeable envelope or cyst. 
En'doderm (Gr. endon, within ; derma, skin) : the inner layer of cells in an 

embryo, giving rise to the digestive tract, etc. 


En'doskeleton (Gr, p.ndon, within ; skeletos, hard) : a skeleton inside the body 
as opposed to the outer or exoskeleton. 

En'dosperm (Gr. endon, within) : food stored in the seed outside the embryo. 

En'ergy (Gr. energos, at work) : work power ; abiHty to perform work. It 
may be latent or kinetic. 

Envi'ronment (Fr. environ, about) : the surroundings of an organism. 

En'zyme (Gr. en, in ; zyme, leaven) : a substance which brings about a chemical 
action, assisting in digestion. 

Epider'mis (Gr. epi, upon ; derma, skin) : an outer layer of cells ; the outside 

Epiglot'tis (Gr. epi, upon ; glotta, tongue) : a covering over the opening into 
the trachea. 

Ero'sion (Lat. erodere, to gnaw off) : the wearing away of rocks by water, 
wind, glaciers, and other agents. 

iSsoph'agus : muscular tube leading from the pharynx to the stomach ; gullet. 

Essen'tial organs : the stamens and pistils, parts of a flower which have to do 
with the production of seeds. 

Eugenics (Gr. eugenes, well born) : the science which deals with race improve- 
ment through heredity. 

Eusta'chian tube : the canal connecting the tympanic cavity with the pharynx, 
named for its discoverer, Eustachio, an Italian physician. 

Euthen'ics (Gr. euthenein, to thrive) : the science which deals with race im- 
provement through betterment of the environment. 

Excre'tion : elimination of waste products from an organism. 

Exoskereton : an outside skeleton. 

Fatigue' (Lat. fatigare, to weary) : the effect produced by prolonged stimula- 
tion on the cells of an organism. 
Fats : a class of nutrients composed of much carbon and hydrogen with a little 

Fermenta'tion (Lat. fermentum, ferment) : the chemical transformation of 

organic substances through the agency of enzymes or ferments, or through 

the agency of bacteria. 
Fertiliza'tion (Lat. fertilis, fruitful) : the union of an egg cell and a sperm cell. 
Fibrovas'cular bundles : collections of tubular cells, supported by woody 

cells, which conduct fiuids^in plants. 
Fin : a fold of skin, with skeletal supports, used for swimming. 
Fis'sion (Lat. fissum, cleft) : division of a cell into two cells of equal size. 
Flagerium (Lat. flagellum, whip) : a vibratory threadlike projection of certain 

Fo'cal inf ec'tion : a center of bacterial infection, often at the base of a tooth, 

from which toxins reach the blood. 
Food : a substance that forms the material for the growth or repair of the 

body of a plant or an animal or that furnishes energy for it. 


Fniit : a ripened ovary together with any parts of the flower adhering to it. 
Func'tion (Lat. functio, performance) : the normal action of an organ or organs. 


Gam'etes : sex cells. 

Gan'glion (pi. Ganglia) (Gr. ganglion, Httle tumor) : a mass of nervous matter 
containing nerve cells which give rise to fibers. 

Gas'tric glands (Gr. gaster, stomach) : digestive glands found in the walls 
of the stomach. 

Gas'trula (Gr. gaster, stomach) : a cuplike structure formed b}^ the invagina- 
tion or turning in of the blastula. 

Geot'ropism (Gr. ge, earth ; tropein, to turn) : response to gravity. 

Germ cells : egg or sperm cells. 

Germina'tion : the beginning of growth in a seed or a pollen grain. 

Gill rakers : small spinelike structures attached to gill arches which prevent 
escape of food. 

Gills : breathing organs for use in water. 

Gland (Lat. glans, an acorn) : an organ which secretes material to be used in or 
excreted from the body. 

Gly'cogen (Gr. glykus, sweet ; -gen, producing) : animal starch, found in the Uver. 

Guard cells : epidermal cells, found on each side of a stoma. 

Gullet (Lat. gula, gullet) : a muscular canal extending from the pharynx to 
the stomach ; the esophagus. 


Habit : an acquired reflex act. 

Haemoglo'bin (Gr. haima, blood ; glohos, sphere) : red coloring matter of the 

Hsemoly'sins : substances in blood which destroy foreign red corpuscles. 
Heliot'ropism (Gr. helios, sun ; tropein, to turn) : response to sunlight. 
Heredity (Lat. heres, heir) : transmission of quaUties from parent to child. 
Hermaphroditic (Gr. hermaphroditos, combining both sexes) : having both 

male and female sex organs. 
Hilum : a scar on the testa left where the seed was attached to the pod. 
Homol'ogy : likeness in structure and position. 
Hor'mones (Gr. hormaein, to excite) : substances produced bj^ some of the 

glands of the body which effect a chemical coordination. 
Hu'mus (Lat. humus, ground) : vegetable mold, a black or dark colored sub- 
stance formed by the decay of organic substances in the soil. 
Hy'brid (Lat. hyhrida, mongrel) : the offspring of parents of two different 

species or varieties. 
Hy'drogen (Gr. hydor, water ; -gen, producing) : a gaseous element foimd in 

water and many other compounds. 
Hy'giene (Gr. hygeia, health) : a study of the preservation of health. 
Hypocot'yl (Gr. hypo, under) : the part of the developing embryo which forms 

the root and the lower part of the stem. 


Imbibi'tion : a form of diffusion that results in the sweUing of material taking 

in a fluid. 
Immu'nity (Lat. immunis, free from duty) : the successful resistance of an 

organism to infections from microorganisms. 
Imperfect flowers : flowers having only one kind of essential organs, either 

stamens or pistils. 
Incubation period : the time after the germs of a disease enter the body untU 

the symptoms of the disease appear. 
Infec'tious : caused by disease-producing organisms, or germs. 
Inher'itance : that which is passed on by heredity. 
In'stinct : a tendency to perform an act which is performed for the first time 

without being learned. 
In'sulin: a hormone produced in " Islands of Langerhans " in the pancreas; 

remedy for diabetes. 
Intes'tine (Lat. intestinus, internal) : the food tube in vertebrates from the 

pyloric end of the stomach to the anus. It is divided into the small and 

the large intestine. 
^'ris (Gr. iris, rainbow) : the colored portion of the eye, having the pupil in the 


Kid'neys : glands which secrete urine. 

fijuiet'ic (Gr. kinein, to move) : energy employed in producing motion. 

Lac'teals (Lat. lacteus, milky) : lymphatic vessels which carry fats and other 

substances from the intestine to the thoracic duct. 
Lar'va (Lat. larva, a ghost) : a young stage in the development of some forms 

of animals, which becomes self-sustaining but which does not have the 

characteristics of the adult. 
La'tent (Lat. latere, to lie hid) : lying dormant but capable of development. 
Leg'umes (Lat. legere, to gather) : plants which bear seeds in pods — peas, 

beans, and the like ; also the fruits or seeds of such plants. 
Len'ticel : a breathing hole in the bark of a tree. 
Lig'ament (Lat. ligare, to bind) : a band of connective tissue binding one bone 

to another. 
Liv'er : a digestive gland which secretes bile. 
Lymph (Lat. lympha, water) : plasma and colorless corpuscles outside of the 

blood vessels. 
Ly'sins (Gr. lysis, a loosing) : antibodies which have power to dissolve bacteria 

in the blood. 

H. NEW CIV. BIOL. — 28 



Macronu'cleus (Gr. makros, large) : the large nucleus, as opposed to the micro- 
nucleus, or small nucleus. 

Mam'mary glands (Lat. mamma, breast) : milk-secreting glands found in mam- 

Man'dible (Lat. viandere, to chew) : in insects, a hard cutting jaw. 

Man'tle (Lat. mantellum, a cloak) : the soft outer fold of skin in mollusks which 
secretes the outer shell. 

Maxilla (Lat. mxixilla, a jaw) : an appendage near the mouth of arthropods, 
modified in insects to form an organ for getting food. 

Maxiriiped (Lat. maxilla, jaw; pes, foot) : an appendage next posterior to the 
maxilla in arthropods. Foot jaw. 

Medulla oblonga'ta (Lat. medulla, pith) : the most posterior part of the brain. 

Med'uUary rays (Lat. medulla, pith) : thin plates of pith which separate the 
wood of dicotyledonous stems into wedge-shaped masses. 

Mes'oderm (Gr. mesos, middle ; dermxi, skin) : the middle layer of cells in a 
young animal embryo. 

Metab'olism (Gr. metaholos, changeable) : changes taking place continually in 
living cells which may result in either building up or breaking down the 

Metamor'phosis (Gr. meta, after ; morphe, form) : change of form undergone 
from egg to adult, as in insects. 

Mic'ropyle (Gr. micropyle, a Httle gate) : the hole where the pollen tube enters 
the embryo sac. 

Mid'rib : central vein of a leaf. 

Mi'grant : an animal which moves from one place to another and back regularly 
at stated seasons of the year. Many birds migrate to warmer regions 
for the winter. 

Mimicry (Gr. mimikos, imitative) : the imitation in form or color of a harm- 
ful insect by a harmless one which is protected thereby. 

Mol'ecules : units of a chemical substance. 

Monocotyle'don : a plant that bears seeds having but one cotyledon. 

Monohy'brid : Mendelian term for a cross between organisms which differ 
in one pair of alternative characters. 

Mu'cous membrane (Lat. mucus, slime ; memhrana, skin) : a delicate, moist 
membrane lining all body passages which have an external opening. 

Mus'cle (Lat. musculus, muscle) : a contractile tissue capable of bringing 
about movement. 

Muta'tion : a heritable modification arising from internal causes in an organism. 

Myce'lium : the threadlike body of a mold, or other fungus, the individual 
threads being called hyphse. 


Narcotic (Gr. narkotikos, making dumb) : a substance which blunts the senses 
and in large quantities causes insensibility. 


Nec'tar (Gr. nectar, drink of the gods) : a sweet fluid secreted by certain 
groups of cells known as nectar glands in a flower. From this substance 
bees make honey. 

Neu'ron : a nerve cell. 

Nic'titating membrane (Lat. nidare, to wink) : the third eyelid, a delicate 
membrane covering the eye in birds and frogs. 

Ni'trate : a soluble salt of nitric acid. 

Ni'trogen (Lat. nitrum, natron ; -gen, producing) : a gaseous element, found 
in many organic compounds and forming almost four fifths of the atmos- 

Nu'cleus (Lat. nucleus, a kernel) : the center of activity in the living cell. 

Nu'trient (Lat. nutrire, to nourish) : nourishing substance contained in foods. 

Nu'tritive ratio : the proportion of protein in the diet. 

Oils : a class of nutrients composed of much carbon and hydrogen, with a 

little oxygen. 
Ommatid'itmi (Gr. omma, eye) : one of the elements of a compound eye. 
Oper'culum (Lat. operculum, a lid) : a lid or flap covering the gills. 
Op'sonin (Gr. opsonein, to cater for) : a substance in the blood which helps 

colorless corpuscles destroy bacteria. 
Organ : each part in an animal or plant which performs some special work. 
Or'ganism (Gr. organon, an instrument) : a body which is made up of organs 

or parts, each of which has a special function ; any animal or plant. 
Osmo'sis : diffusion of water through a semi-permeable membrane, the greater 

flow being toward the lesser concentration of water. 
O'vary (Lat. ovum, egg) : in a plant, the base of a pistil, containing the ovules ; 

in an animal, the egg-forming gland. 
Ovipos'itor (Lat. ovum, egg ; ponere, to place) : a specialized structure for 

depositing eggs, found in insects. 
O'vule : a rounded structure in the ovary, which may become a seed. 
Oxida'tion : the chemical union of oxygen with some other substance. 
Ox'ygen (Gr. oxus, acid ; -gen, producing) : a gaseous element found in the 

air and in many compounds. 
Oxyhaemoglo'bin : a combination of oxygen with haemoglobin. 

Pal'ate (Lat. palatum) : the roof of the mouth. The hard palate is sup- 
ported by bone ; the soft palate is a fold of mucous membrane lying pos- 
terior to the hard palate. 

Palisade layer : a layer of green cells under the upper epidermis of a leaf. 

Pal'pus or palp (Lat. palpare, to touch) : in arthropods, an appendage at- 
tached to a mouth part ; usually an organ of touch or taste. 


Pan'creas (Gr. pan, all ; kreas, flesh) : a digestive gland. It secretes pan- 
creatic juice. 

Pap'pus : a downy or fluffy outgrowth from the ovary wall. 

Par'asite : an organism which secures its living directly from another living 
organism without giving anything in return, 

Pas'teurize (from Pasteur the scientist, p. 408) : to heat milk to about 140° 
Fahrenheit for about 20 minutes for the purpose of killing bacteria in it. 

Pathogenic organisms : bacteria or protozoa which cause disease. 

Pec'toral girdle (Lat. pectoralis, pertaining to the breast) : bones which sup- 
port the anterior pair of appendages in vertebrates. 

Pel'vic girdle (Lat. pelvis, a basin) : the bony arch to which the posterior 
pair of appendages are attached in vertebrates. 

Peristal'tic (Gr. peristellein, to surround) : wavelike movements of the muscles 
of the food tube. 

Pet'al : one of the leaflike parts of the corolla. 

Pet'iole (Lat. petiolus, a little foot) : the stalk of a leaf. 

Phag'ocyte (Gr. phagein, to eat ; kytos, cell) : a colorless corpuscle which de- 
stroys bacteria. 

Phar'ynx (Gr. pharynx, gullet) : an irregular cavity at the back of the mouth. 

Phloem : that part of the fibrovascular bundle which contains the sieve tubes. 

Photosyn'thesis (Gr. phos, light; synthesis, a putting together) : the pro- 
cess of making starch out of carbon dioxide and water by the aid of sun- 
light, as is done by a green cell. 

Photot'ropism : reaction to light. 

Phylum : a large division of the plant or the animal kingdom. It is com- 
posed of classes. 

Physiological division of labor : performance of different kinds of work by 
different parts of an organism. 

Physiorogy (Gr. physis, nature ; logos, discourse) : study of the functions 
of plants and animals. 

Pislil: a structure in the flower containing the ovary, in which the seeds 
are formed. 

Pith : the soft, spongy tissue in the center of a dicotyledonous stem and be- 
tween the vascular bundles of a monocotyledonous stem. 

Placen'ta (Lat., placenta, cake) : absorbing organ which nourishes the embryo. 

Plank'ton : small plants a^d animals which live near the surface of bodies of 

Plas'ma (Gr. plasma, anything formed or molded) : the colorless fluid part 
of blood. 

Pleu'ra (Gr. pleura, the side) : the membrane which covers the lungs and 
lines the cavity containing them. 

Plu'mule : the part of the embryo above the cotyledons which develops into 
the stem and leaves. 

Pollen grain : a structure in flowers which contains the sperm cell or male 


Pollina'tion : the transfer of pollen from the anther to the stigma. Self- 
pollination is transfer between parts in the same flower ; cross-pollination 
is transfer between different flowers, or between flowers on different plants. 

Poryp (Lat. polypus, a polyp) : a simple actinozoan, as a sea anemone or a 
single coral individual. 

Poste'rior (Lat. posterior, later) : nearer the last or tail end of an animal. 

Precip'itins : antibodies or precipitating substances formed in the blood as a 
reaction to the introduction of certain foreign proteins. 

Probos'cis (Gr. pro, before ; hoskein, to feed) : a slender sucking tube found 
in insects. 

Proglot'tids (Gr. pro, forward ; glotta, tongue) : reproductive body segments 
of a tapeworm. 

Pro leg : an un jointed abdominal appendage of insect larvae. 

Protec'tive resemblance : the likeness of living organisms in color or form 
to their immediate surroundings, thus securing protection from attack 
of enemies. 

Pro'teins (Gr. protos, first) : nitrogenous compounds found in the bodies of 
plants and animals; a class of nutrients composed of nitrogen, carbon, 
hydrogen, and oxygen, together with other elements in some cases. 

Pro'toplasm (Gr. protos, first ; plasma, a thing formed) : the living substance 
of plants and animals. 

Protozo'a (Gr. protos, first ; zoon, animal) : one-celled animals. 

Pseudopo'dium (Gr. pseudes, false ; pous, foot) : a projection of protoplasm 
used for locomotion in protozoa. 

Pto'maine (Gr. ptoma, a corpse) : poisonous material probably the result of 
decomposition of proteins. 

Pul'monary (Lat. pulmo, lung) : pertaining to the lungs. 

Pulvi'nus (Lat. pulvinus, cushion) : a special motor organ at the base of the 
petiole of a leaf. 

Pu'pa (Lat. pupa, puppet) : the quiescent stage in insect development pre- 
ceding the adult. 

Pylo'nis (Gr. pyloros, gatekeeper) : the opening of the stomach into the in- 


Quar'antine (Fr. quarante, forty, referring to 40 days quarantine against 
plague in Venice and other Italian cities during the Middle Ages) : isola- 
tion of the sick to prevent the spread of commxmicable disease. 

Re'flex : simplest type of nervous response. 

Regenera'tion (Lat. re, again ; generare, to beget) : the growing again of a 

part of an animal which has been lost. 
Reproduc'tion : the process by which organisms produce offspring. In 

asexvul reproduction a new organism is formed by the separation of a 


cell or cells from a single parent ; in sexual reproduction two cells from 

two plants or two animals of different sexes come together to form a new 

Respira'tion (Lat. re, again ; spirare, to breathe) : taking in oxygen and giving 

out carbon dioxide by living cells. 
Ret'ina (Lat. rete, a net) : the coat of the eye in which the optic nerve fibers 

Rhi'zoids (Gr. riza, root) : root-like bodies in fungi and some other plants. 

Sali'va (Lat. saliva, spittle) : the secretion of the salivary glands. 
Sap'rophyte (Gr. sapros, rotten ; phyton, plant) : an organism which derives 

its nourishment from dead organic matter, as a mold or a mushroom. 
Sclerot'ic coat (Gr. skleros, hard) : the outer coat of the eye. 
Secre'tin : a hormone which causes the pancreas to give out its digestive fluid, 
Secre'tion : material formed by the activity of glands. 
Seed : a structure formed in a fruit as a result of the fertilization of the egg 

Seg'ment (Lat. segmentum, a piece cut off) : one of a number of serial divi- 
sions of an animal's body or of an organ. 
Sen'sory (Lat. sensus, feeling) : having direct connection with any part of 

the seat of sensation. 
Se'pal : a leaflike part of the calyx or outer circle of parts in a flower. 
Se'rum : the Hquid part of the blood plasma. 
Se'tae (Lat. seta, a bristle) : bristles used for locomotion in earthworms and 

other animals. 
Sex'ual (Lat. sexus, sex) : pertaining to or having sex. 
Si'phon (Gr. siphon, a tube) : a tube through which water may pass into and 

out from the mantle cavity of a mollusk. 
Spe'cies : the smallest group of organisms having characteristics in common 

that make them different from all other organisms. 
Sperm cell : the male sex cell or gamete. 

Spi'nal cord : a cord of nervous tissue lying in the vertebral column. 
Spir'acles (Lat. spiraculum, breathing hole) : breathing holes in insects. 
Spirillum (Lat. spira, coil) : a spiral form of bacteria. 
Spleen : ductless, glandlike organ near the stomach. 
Spongy tissue : a layer of loosely placed cells in the leaf. 
Sporan'gium (Gr. sporos, a seed ; angeion, a vessel) : a sac containing spores. 
Spore : a reproductive cell capable of growing into a mature organism. It 

may be produced sexually or asexually. 
Spo'rophyte (Gr. sporos, seed ; phyton, plant) : spore-bearing part of a plant. 
Sta'men : an organ of the flower in which pollen is formed. 
Stat'ocyst : semi-organs or balancing pits, formed in crustaceans and some 

other animals. 


Ster'ilize (Lat. sterilis, barren) : to destroy bacteria and other organisms, 
usually by heating. 

Stig'ma (Gr. stigma, the prick of a pointed instrument) : the part of a pistil 
which receives the pollen grains. 

Stim'ulant (Lat. stimulus, a goad) : a substance which causes temporary ac- 
tivity of nerve or muscle. 

Stim'ulus (Lat. stimulare, to incite) : an agent which causes an organism or 
some part to react when affected by it. 

Stip'ule (Lat. stipula, stem) : a leaflike outgrowth at the base of the petiole. 

Sto'ma (pi. Sto'mata) (Gr. stomu, a mouth) : a breathing hole in a leaf. 

Stom'ach (Gr. stomachos, throat) : a sac-like part of the food tube between 
gullet and intestine. 

Suc'cus enter'icus : fluid secreted by glands in the small intestine, an aid to 

Sweat glands : excretory glands in the skin. 

Swim'merets : paired appendages on the abdomen of crustaceans. 

Symbio'sis (Gr. symbiosis, a living together) : a condition in which two organ- 
isms of different kinds live together in a mutually beneficial partnership. 

Synapse' : contact between the end arborization of one neuron and the den- 
drites of another neuron. 

Tac'tile corpuscle (Lat. tangere, to touch) : sense organ of touch. 

Tar'sus (Gr. tarsos, sole of foot) : the ankle bones ; also the last region of the 
leg of an insect. 

Taste bud : end organ of taste found on the tongue. 

Teeth : limy structures in the mouth of man and other animals, consisting 
of incisors or cutting teeth ; canines, tearing teeth ; and molars and pre- 
molars, crushing and grinding teeth. 

Ten'don (Lat. tendere, to stretch) : a band of connective tissue attaching mus- 
cle to muscle or muscle to bone. 

Ten'tacle (Lat. tentaculum, a feeler) : a flexible organ at the anterior end of 
an animal used for feeling, grasping, etc. 

Tes'ta : the thick outer coat of a seed. 

Tes'tes (Lat. testis) : sperm-producing glands. 

Thorac'ic : pertaining to the chest region. 

Tho'rax (Gr. thorax, the chest) : the part of the body between the head and 
the abdomen. 

Tissue (Fr. tissu, a web) : a collection of cells all more or less alike and having 
the same function. 

Tox'ins : poisons produced by bacteria. 

Tra'chea (Lat. trachia, windpipe) : the windpipe ; also a respiratory tube 
of insects. 

Transpira'tion (Lat. trans, through ; spirare, to breathe) : the giving off of 
water vapor from plants. 


Trichi'na: pork worm, a parasitic roundworm causing the condition called 

Tro'pism (Gr. tropein, to turn) : a definite response of an organism to one of 

the forces in its environment. 
Tryp'anosomes (Gr. trypanon, an auger) : protozoa which cause disease such 

as sleeping sickness. 
Tym'panum (Gr. tympanon, a drum) : the eardrum. 


U'rea (Lat. urina, urine) : a nitrogenous waste excreted in the urine. 

Vaccina'tion : inoculation with a vaccine, containing living or dead micro- 
organisms or their toxins, in order to protect the body from disease. 

Vac'cine : a substance made from living or dead organisms, which, when inoc- 
ulated into the body, protects against a specific disease. 

Vac'uole (Lat. vacuus, empty) : a space in protoplasm containing air, water, 
sap, or food material. 

Varia'tion: in biology, the occurrence of differences between individuals of 
the same species. 

Vein : a tube which conveys blood to the heart. 

Ve'nae ca'vae : vessels through which the blood returns to the right auricle 
of the heart. 

Ventila'tion (Lat. ventilare, to air) : changing of air in a room or building. 

Ven'tral (Lat. venter, belly) : the opposite of dorsal. 

Ven'tricle (Lat. ventriculus, a little belly) : a muscular chamber of the heart, 
which forces the blood out. 

Ver'mifonn appendix (Lat. vermis, worm) : a narrow tube about four inches long, 
closed at the outer end, near the beginning of the large intestine of man. 

Ver'tebrae (Lat. verier e, to turn) : bones of the vertebral column. 

Ver'tebrate : an animal having a backbone. 

Villus (Lat. villus, shaggy hair) : a minute projection, an absorbing organ 
of the small intestine. 

Vi'tamin (Lat. vita, life) : unknown substances in food apparently necessary 
to support life. 

Voruntary (Lat. voluntas, will) : subject to the will (used with reference to 
muscles), as opposed to involuntary. 


Xy'lem (Gr. xylon, wood) : the inner woody part of a fibrovascular bundle 
which conducts water up the stem, 


Zy'gospores or Zy'gotes : spores formed by union of sex cells. 


As the metric system of weights and m.easures and the Centigrade measurement 
of temperatures are employed in scientific work, the following tables showing the 
English equivalents of those in most frequent use are given for the convenience of 
those not already familiar with these standards. The values given are approximate 
only, but will answer for all practical purposes. 







2^ pounds 

15| grains avoir- 

5g of an ounce 


Cubic cen- 
timeter . 

a little more than 
1 quart, U. S. 


of a cubic inch. 


OF Length 


English Equivalents 



f of a mile. 

Meter . . 


39 inches. 



4 inches. 



1 of an inch. 



5^ of an inch. 

The next table gives the Fahrenheit equivalent for every tenth degree Centigrade 
from absolute zero to the boiling point of water. To find the corresponding F. for 
any degree C, multiply the given C. temperature by nine, divide by five, and add 
thirty-two. Conversely, to change F. to C. equivalent, subtract thirty-two, multi- 
ply by five, and divide by nine. 







Cent. Fahb. 

100 . 
90 . 
80 . 

. 212 
. 194 
. 176 
. 158 
. 140 

50 . 
40 . 
30 . 
20 . 
10 . 

. 122 
. 104 
. 86 
. 68 
. 50 

. . 
-10 . . 
-20 . . 
-30 . . 
-40 . . 

. 32 
. 14 
. - 4 
. -22 
. -40 

- 50 . . . - 58 

- 100 . . . - 148 

70 . 
60 . 

Absolute zero 
- 273 . , . - 459 


Laboratory Equipment 

The following articles comprise a simple equipment for a laboratory class of 
ten. The equipment for larger classes is proportionately less in price. The follow- 
ing articles may be obtained from any reliable dealer in laboratory supplies, such as 
the Bausch and Lomb Optical Company of Rochester, N.Y., or the Central Scientific 
Company, 460 East Ohio Street, Chicago, 111. 

1 balance, Harvard trip style, with weights on carrier. 

1 bell jar, about 365 mm. high by 165 mm. in diameter. 
10 wide mouth (salt mouth) bottles, with corks to fit. 

10 25 c.c. dropping bottles for iodine, etc. 
25 250 c.c. glass-stoppered bottles for stock solutions. 
100 test tubes, assorted sizes, principally 6" X |". 
50 test tubes on base (excellent for demonstrations). 

2 graduated cylinders, one to 100 c.c, one to 500 c.c. 

1 package filter paper 300 mm. in diameter. 
10 flasks, Erlenmeyer form, 500 c.c. capacity. 

2 glass funnels, one 50, one 150 mm. in diameter. 

30 Petri dishes, 100 mm. in diameter, 10 mm. in depth. 
10 feet glass tubing, soft, sizes 2, 3, 4, 5, 6, assorted. 

1 aquarium jar, 10 liters capacity. 

2 specimen jars, glass tops, of about 1 liter capacity. 
10 hand magnifiers, vulcanite or tripod form. 

2 compound demonstration microscopes or 1 more expensive compound micro- 
300 insect pins, Klaeger, 3 sizes assorted. 
10 feet rubber tubing to fit glass tubing, size f inch. 

1 chemical thermometer graduated to 100° C. 
15 agate ware or tin trays about 350 nam. long by 100 wide. 
1 gal. 95 per cent alcohol. (Do not use denatured alcohol.) 
1 set gram weights, 1 mg. to 100 g. 2 books test paper, red and blue. 

1 razor, for cutting sections. 10 Syracuse watch glasses. 

1 box rubber bands, assorted sizes. 1 steam sterilizer (tin will do). 

1 support stand with rings. 1 spool fine copper wire. 

1 test tube rack. 1 alcohol lamp. 6 oz. nitric acid. 

5 test tube brushes. 1 gross slides. 6 oz. ammonium hydrate. 

10 pairs scissors. 100 cover slips No. 2. 6 oz. benzole or xylol. 

10 pairs forceps. 1 mortar and pestle. 6 oz. chloroform. 

20 needles in handles. 2 bulb pipettes. | ib. copper sulphate. 

10 scapels. 1 liter formol. ^ lb. sodium hydroxide. 

12 mason jars, pints. 1 oz. iodine cryst. ^ lb. rochelle salts. 

12 mason jars, quarts. 1 oz. potassium iodide. 6 oz. glycerine. 

The agar or gelatine cultures in Petri dishes may be obtained from the local Board 
of Health or from any good druggist. These cultures are not difficult to make, but 
take a number of hours' consecutive work, often difficult for the average teacher to 
obtain. Full directions how to prepare these cultures will be found in Hunter's 
Laboratory Problems in Civic Biology. 


(Illustrations are indicated by page numerals in bold-face type.) 

Abdomen, of insect, 25. 
Abilities, natural, 402-403. 
Absorption, of food, 157, 158. 
Accommodation, of eye, 206. 
Acetanilid, poison, 144. 
Adam's apple, 178. 
Adaptations, 19-20; 

in a bee, 33 ; 

in birds, 247 ; 

in frogs, 109 ; 

in mammals, 237, 249. 
Adenoids, 182, 310. 
Adrenaline, 167. 
Adrenals, 167. 
Adrenine, 167. 
Adulteration, 138, 139. 
Aedes, 281. 
Agglutinin test, 166. 
Agglutinins, 165, 276. 
Air, change of, 186 ; 

composition of, 8, 179 ; 

needed by man, 177 ; 

needed by plants, 57, 58, 82. 
Alcohol, dangers from, 141-142 ; 

economic effect, 214; 

effect on the blood, 175 ; 

food, 139-140; 

in patent medicines, 143 ; 

poison, 140; 

relation to crime, 216 ; 

relation to efficiency, 215, 216 ; 

relation to heredity, 217. 
Alg«, 223, 236. 
Alimentary canal, 147. 
Alligator, 366. 

Alternation of generations, 228. 
Amino-acids, 120, 158. 
Amoeba, 99, 100; 

and Paramecium, 108; 

receives stimuli, 193. 
Amphibia, 243, 246. 

Amylase, 150, 155. 
Anaerobic bacteria, 258. 
Analogy, 238. 
Ancon ram, 385. 
Angiosperms, 237. 
Animals, 98-100, 108-111; 

breeding of, 384, 385-389, 391, 392; 

cell, typical, 46, 49 ; 

classification of, 238 ; 

disease-causing, 278-290 ; 

diversity of form, 43 ; 

domesticated, 353, 391, 392 ; 

economic importance, 347-366 ; 

fibers, 353,354; 

food of man, 347-353 ; 

harmful, 278-290, 361, 362, 366; 

influence of environment, 14-21 ; 

organs and functions of the higher, 

primary needs, 107 ; 

relation to man, 3-4, 5, 278-290, 

relation to plants, 4, 30-31, 35, 40, 

reproduction in, 220, 222, 226-232 ; 

responses in, 192-193, 195, 196 ; 

simplest, 95; 

summary of the functions, 92-94 ; 

unselfishness, 6. 
Annual rings, 88. 
Annulata, 240, 241. 
Anopheles, 279, 280. 
Antennae, 26, 196. 
Anther, defined, 32. 
Anthrax, 266, 271. 
Antibodies, 165-166, 271, 272, 276; 

effect of alcohol, 175. 
Antiseptics, used by Lister, 410. 
Antitoxin, 272, 273, 274. 
Anura, 246. 
Aorta, 170. 




Apoplexy, 175. 

Appendages, of frog and man, 109. 

Appendix, vermiform, 159. 

Appetite, for foods, 128, 130. 

Apple, 41, 329. 

Aptera, 242. 

Aquarium, balanced, 102, 103, 348. 

Arachnida, 242. 

Arbor Day, 321. 

Argj-rol, 214. 

Arteries, 169, 172, 173; 

hardening of, 174. 
Arteriosclerosis, 174. 
Arthropoda, classified, 241, 242. 
Artificial respiration, 183. 
Artificial selection, 384. 
Ascaris, 288, 289. 
Asexual reproduction, defined, 222 ; 

in animals, 228 ; 

in plants, 222, 223. 
Ashes, disposal of, 306, 307. 
Assimilation, 15, 93. 
Astigmatism, 213. 

Atwater, authority on foods, 132, 139. 
Auditory nerve, 205. 
Audubon, cited, 375. 
Auricle, 169, 170, 171. 
Autonomic nervous system, 200, 201. 
Aves, 243. 
Axon, 198. 

Bacillus, 96, 256. 
Bacteria, 256-258; 

affected by light and air, 258 ; 

and disease, 3, 253, 260-276; 

as simple plants, 96 ; 

carried by dust, 297 ; 

cause decay, 339, 340 ; 

cause fermentation, 340 ; 

cause skin infection, 113; 

control of, in food, 343-345 ; 

disinfection, 259; 

for study, 254, 255, 256; 

in breadmaking, 339 ; 

in fluids, 257 ; 

in food, 299; 

in hay infusion, 97 ; 

in milk, 259, 300-303, 340; 

in water supply, 303 ; 

nitrogen-fixing, 104, 341; 

Bacteria, reproduction, 256; 

size and form, 256 ; 

sterilization, 258; 

useful, 3, 340, 341 ; 

where found, 255, 256-257; 

work of Pasteur, 408, 409. 
Bacteriology, defined, 3. 
Balanced aquarium, 102, 103, 348. 
Balancing function of ear, 196-197, 

Banting, Dr., work on insulin, 168. 
Bark, described, 87, 88, 89. 
Barley, 328. 
Barrier, natural, 20, 21. 
Basal metabolism, 132-133. 
Bast fibers, described, 87, 89 ; 

used by man, 330, 331. 
Beans, germination of, 55-58, 56 ; 

growth, 51-58; 

pod and seed, 52 ; 

position of leaves, 194 ; 

value as food, 124. 
Bedbug, 27, 283, 286. 
Bedroom, care of, 293 ; 

ventilation, 184-185. 
Bee, 25, 26 ; 

adaptations, 33, 34; 

life, 351. 
Beehive, 351. 

Beetles, 27, 28, 357, 362, 364. 
Beets, 324, 325. 
Benedict's test, 60. 
Benzoic acid, 345. 
Beriberi, deficiency disease, 123. 
Beverages, 329. 

Bichloride of mercury, 259, 260. 
Bile, 156. 
Biology, study of, 1 ; 

relation to society, 6. 
Birds, 247-248; 

as food, 353 ; 

bills and feet, 247 ; 

brain, 200 ; 

classification of, 248 ; 

conservation of, 375-378; 

eat insects, 359 ; 

eat weed seeds, 360 ; 

migrations, 376, 377 ; 

reproduction, 231, 232; 

useful and harmful, 360. 



Bison, 248. 

"Black Hole of Calcutta," 183. 

Bladder, offish, 245; 

urinary, 188. 
Blastula, 227. 
Blood, changes in the lungs, 178 ; 

circulation of, 169-174, 171 ; 

clotting of, 121, 164-165 ; 

composition of, 11, 162-168; 

four types of, 166 ; 

pressure, 173, 174; 

transfusion, 166. 
Blood plates, 165. 
Blood pressure, 173, 174. 
Board of health, 268, 272, 308-311. 
Bobolink, 360, 377. 
Body, a machine, 110, 111, 208; 

cavity, 116; 

composition of, 10 ; 

temperature, 189; 

value of understanding, 112. 
Boils, 276. 

Boll weevil, 362, 363. 
Bones, human, 114. 
Borax, preservative, 345. 
Bordeaux mixture, 337. 
Boveri, biologist, 413. 
Bracket fungus, 335. 
Brain, fatigue, 212; 

of animals, 200 ; 

of man, 199. 
Bread, value as food, 120, 124. 
Bread making, 339. 
Breathing, 180, 181; 

hygienic habits, 181 ; 

of birds, 247; 

of frogs, 110, 111; 

of leaves, 85-86, 
Brittle star, 241. 
Broadhurst, Dr., tests of dishwashing, 

Bronchi, 178. 
Bronchial tubes, 178. 
Bruises, treatment of, 175. 
Bryophytes, 236. 

Bubonic plague, 266, 285, 286, 287. 
Budding, propagation by, 221 ; 

reproduction by, 223 ; 

reproduction of animals, 228. 
Buffalo, or bison, 248, 377. 

Bugs, 27, 363, 364. 
Bumblebee, 33, 35. 
Burbank, Luther, 390, 414. 
Bureau of Entomology, 365. 
Burns, 113. 

Butter and eggs, 34, 35. 
Butterflies, 26; 

life history, 28, 29, 30, 229 ; 

pollination by, 38. 

Cabbage, 324. 
Cabbage butterfly, 229. 
Caffein, 139. 
Calcium, as a food, 121. 
Calorie, defined, 119; 

food requirement, 132-134. 
Calorimeter, 119. 
Calyx, defined, 31, 32. 
Cambium layer, 88, 90. 
Camera, compared with eye, 205, 206. 
Canning, 343, 344. 
Capillaries, 169, 172, 173. 
Capillarity, explained, 65. 
Carbohydrates, amount needed daily, 

described, 53, 119; 

foods containing, 124. 
Carbolic acid, 260. 
Carbon, 10-11. 
Carbon cycle, 103. 
Carbon dioxide, in respiration, 179 ; 

in starch making, 82 ; 

test for, 11. 
Carnivora, 249. 
Carrell, investigator, 411. 
Carriers, of disease, 264, 265, 301 ; 

insects, 279, 281, 283, 284, 285 ; 

rats, 286. 
Carrot, 325. 
Catarrh, 181. 
Caterpillar, 29. 
Cats, damage from, 366, 376. 
Cattle, 353. 
Celery, 324. 
Cells, 44; 

division of, 47, 48, 99, 100, 219, 220 ; 

functions, in one-celled animals, 

plant and animal contrasted, 46, 



Cells, respiration, 179, 180; 

sizes and shapes, 49 ; 

structure of, 45-46 ; 

supply of lymph, 168. 
Centipede, 28, 241. 
Centrosomes, 48. 
Cereals, 325-328; 

value as food, 120, 123, 124, 129. 
Cerebellum, 199, 201. 
Cerebro-spinal meningitis, 266. 
Cerebrum, 199, 201. 
Cesspools, 265, 296. 
Cestodes, 287. 
Cetacea, 249. 
Chalk, 355. 
Change of air, 186. 

Characters, inheritable, 388, 397, 401. 
Cheese, flavored by bacteria, 340; 

flavored by mold, 336. 
Cheiroptera, 249. 
Chelonia, 247. 
Chemical compounds, 9. 
Chemical elements, 8. 
Chemist's view of the environment, 

Chemotropism, 17. 
Chestnut bhght, 318, 335. 
Chewing of food, 152, 159. ' 
Chicago, drainage canal, 305, 348. 
Chicken cholera, 274. 
Chicken pox, 269. 
Chitin, of insect, 25. 
Chittenden, Professor, cited, 132, 140. 
Chloride of hme, 260. 
Chlorophyll, 45, 81. 
Chloroplasts, 45, 81; 

work of, 82, 83. 
Chocolate, value as food, 139. 
Cholera, 266, 276. 
Chromosomes, 46; 

bearers of heredity, 381, 383, 396 ; 

in cell division, 47, 48 ; 

sex-determining, 383. 
ChrysaHs, 29, 229. 
Ciha, 96, 98. 
Circulation of the blood, 169-174, 171 ; 

discovery of, 406 ; 

effect of exercise on, 174 ; 

portal, 172. 
Citizenship, lessons of biology, 6. 

City, environment, 21, 22; 

health problems, 298-311; 

need of trees, 320. 
Civihzation, 250, 394; 

and cereals, 325. 
Clams, 349, 361, 371. 
Class, in classification, 235. 
Classification of plants and animals, 

Clothing, discussed, 187. 
Clotting of blood, 121, 164-165. 
Clover, aid to soil fertility, 341, 342 ; 

change in position of leaves, 194. 
Coal, 57. 

Cocaine, 143, 144, 331. 
Coccus, 96, 256. 
Cochineal, 357. 
Cochlea, 204. 
Cockroach, 27, 364. 
Cocoa, 139. 

Cod liver oil, value as food, 123. 
Codfish, 352, 372. 
Codling moth, 363. 
Ccelenterata, classified, 239, 240. 
Coelhelminthes, 241. 
Coffee, 139. 
Cold storage, 343. 
Colds, 190, 264, 298; 

communicable, 190, 268. 
Coleoptera, 27, 28, 242. 
Colorless corpuscle, 163, 164, 168, 174 ; 

effect of alcohol, 175. 
Communicable diseases, work of 

health board, 309. 
Compound, defined, 9. 
Condiments, 128, 329. 
Conjugation, 223. 
Conifers, 237. 
Conservation, 368-379; 

methods of, 369 ; 

of birds, 375-378; 

offish, 370; 

of forests, 369, 370; 

of mammals, 377-378. 
Constipation, 159. 
Contractile vacuoles, 98. 
Coppice growth, 320. 
Coral, 356. 
Corn, germination, 58-60; 

pollination, 39; 



Corn, production, 326, 327; 

stem, 89, 90; 

tests, 54, 55, 59. 
Corolla, 31, 32. 
Corpuscles, blood, 163, 164 ; 

colorless, 163, 164, 168, 174, 175. 
Cotton, 2, 330. 
Cotton-boll weevil, 362, 363. 
Cotyledons, 52, 56. 
Cowpox, 274. 
Cows, 392. 
Crab, 241, 350. 
Cranium, 114. 
Cretinism, 166. 
Cricket, 27. 
Crocodile, 246, 366. 
Crocodilia, 247. 
Crops, rotation of, 341, 342. 
Cross-pollination, 35-39. 
Croton bugs, 295. 
Crow, 359, 360. 
Crustacea, 242, 349. 
Ctenophora, 240. 
Culex, 279, 280. 
Culture medium, 254, 
Cushing, Dr. Harvey, cited, 167. 
Cuts and bruises, treatment, 175. 
Cutworm, 362. 
Cycads, 237. 

Dairies, 4. 

Dandelion leaves, 80. 

Darwin, Charles, life, 411, 412; 

on heredity and variation, 383, 384 ; 

on pollination, 36. 
Decay, caused by bacteria, 339, 

Deforestation, result of, 314. 
Dendrites, 198. 
Department of Agriculture, 365, 390, 

Dermis, human, 112. 
Determiners of characters, 381. 
De Vries, Hugo, 385, 413. 
Diabetes, 168. 
Diaphragm, 116, 147, 180. 
Diastase, 60. 
Diatoms, 236. 
Dick test, 273. 
Dicks, investigators, 411. 

Diet, daily fuel needs, 132-134; 

mixed diet, 132 ; 

properly balanced, 134 ; 

relation of age to, 129 ; 

relation of appetite to, 130 ; 

relation of cost of food to, 130 ; 

relation of digestibility to, 129, 130 ; 

relation of environment to, 128 ; 

relation of sex to, 129 ; 

relation of work to, 128 ; 

relation to kidneys, 188 ; 

table of 100-Calorie portions, 135. 
Dietary, 120-137. 
Diffusion, explained, 70; 

physiological importance, 73. 
Digestibility of foods, 129, 130. 
Digestion, in animals, 61, 110; 

in man, 116, 147-160; 

in plants, 60, 61, 91, 92, 93, 146; 

purpose of, 146-147. 
Digestive tract of frog and man, 

Dihybrids, 389. 

Diphtheria, 263, 269, 272, 273. 
Dipnoan, Dipnoi, 245, 246. 
Diptera, 27, 242. 
Disease, cause of, 254; 

caused by bacteria, 3, 260-266 ; 

caused or carried by animals, 278- 

communicable and uncommuni- 
cable, 216, 268; 

germ or infectious, 261 ; 

how communicated, 261 ; 

immunity to, 270-276 ; 

incubation period, 269, 270; 

infectious, 254, 261 ; 

relation to alcohol, 140, 142 ; 

resistance against, 271 ; 

resisted by antibodies, 165. 
Dishes, washing of, 295. 
Disinfection, 259. 
Division of labor, physiological, 108- 

Dogs, 391 ; 

skeleton, 243. 
Domesticated animals, 353, 391, 392. 
Dominance, law of, 388. 
Dominant characters, 388, 389, 397. 
Dorsal, 243. 



Drink habit, 214. 

Drowning, artificial respiration, 183. 

Drugs, use and abuse of, 143-144. 

Ducks, wild, 376. 

Ductless glands, 166, 167. 

Duff, 318. 

Dusting, proper method, 293-294, 

297, 337. 
Dysentery, 266, 274. 
Dyspepsia, 159, 160. 

Ears, 203, 204; 

of frog, 110; 

used for balancing, 196-197, 204. 
Earthworms, grafting, 221. 
Eating, habits of, 159, 160. 
Echinodermata, classified, 241. 
Echinoderms, as food, 348. 
Ectoderm, 227. 
Eczema, 272. 
Edentata, 249. 
Egg cell, development, 381, 382, 

Eggs, 223,224,225,226; 

fertihzed, 226, 227; 

fish, 372, 373, 374. 

formation of hen's egg, 231 ; 

value as food, 121, 123, 129. 
Egret, 375. 
Ehrhch, Paul, work on immunity, 

Elasmobranch, Elasmobranchii, 245, 

Element, defined, 8, 
Elephantiasis, 289. 
Elodea, 45, 46. 
Embryo, chick, 231, 232; 

of mammal, 232 ; 

of plants, 51-58, 93, 226. 
Embryo sac, of plant, 225. 
Emulsion, 155. 
Endocrine glands, 166, 167. 
Endoderm, 227. 
Endoskeleton, 243. 
Endosperm, 58, 226. 
Engine, compared with body, 112, 
177, 208, 253 ; 

compared with living organism, 118 ; 

energy released in, 56. 
English sparrow, 360. 

Environment, 7-8; 

influence on living things, 14-22 ; 

of man, 21-22, 292-311, 395; 

of plants and animals, 7, 14-22. 
Enzymes, 60, 148; 

in intestine, 155, 157; 

in plants, 91, 92; 

of bacteria, 336 ; 

of yeast, 338. 
Ephemerida, 242. 
Epicotyl, 52. 
Epidermis, human, 112; 

of a leaf, 76; 

of onion, 45. 
Epiglottis, 150, 151. 
Epithelial, layer, in blood vessels, 169 ; 

in viYli, 158. 
Equilibrium, function of ear, 196-197, 

Erepsin, 157. 
Erosion, of soil, 314. 
Esophagus, in man, 152. 
Eugenics, 398. 
Euglena, 193. 
Eustachian tube, 150, 204. 
Euthenics, 395. 
Evaporation from leaves, 75, 76, 77, 

Evergreens, 237. 
Excretion, in man, 111, 187, 188, 189; 

in plants, 93. 
Exercise, 174, 186. 
Exoskeleton, 243; 

offish, 245; 

of insect, 25. 
Experiment stations, 365, 390. 
Eyes, 205, 206 ; 

care of, 213, 214, 310; 

of frog, 110: 

of insect, 26, 33. 

Fabre, entomologist, 209. 
Factories, inspection, 298-299. 
Fallowing, 342. 
Family, in classification, 235. ' 
Fatigue, 174, 186; 

of brain, 212; 

of nerve cells, 212. 
Fats, 53, 119; 

absorption, 158; 



Fats, amount needed daily, 132 ; 

digestion of, 155 ; 

fuel value, 119-120; 

made in the leaf, 83. 
Feeble-mindedness, 399, 400. 
Fehling's solution, 59. 
Fermentation, 338; 

by bacteria, 339, 340 ; 

by yeast, 337-339. 
Fern plants, 236. 
Fertilization, 226, 227; 

of fish eggs, 373, 374; 

see also Pollination. 
Fertilizers, 342. 
Fever, cause of, 190. 
Fibers, vegetable, 330. 
Fibrin, 164, 165. 
Fibrinogen, 164, 165. 
Fibrovascular bundles, in roots, 68 : 

in stem, 89. 
Fig, pollination, 38. 
Filament, 32. 
Filaria, 289. 
Filter beds, 304, 306. 
Fins, of a fish, 243, 244. 
Fisher, Dr. Irving, cited, 134, 262. 
Fishes, 243, 244, 245; 

artificial propagation, 374 ; 

brain, 200 ; 

circulation, 171, 245; 

classified, 245-246 ; 

conservation, 320-375 ; 

development of young, 374-375 ; 

digestive organs, 244, 245 ; 

egg-laying habits, 372, 373 ; 

fins, 244 ; 

food for man, 352 ; 

food of, 348, 361 ; 

gills, 244 ; 

heart, 245; 

migration, 372; 

swim bladder, 245. 
Fiske, John, quoted, 325. 
Fission, of amoeba, 100 ; 

of bacteria, 256 ; 

of Paramecium, 99. 
Flagella, of bacteria, 96 ; 

of Euglena, 193. 
Flatfoot, 115. 
Flatworms, 220, 240. 

Flax, 330. 

Fleas, 285, 286. 

Fletcher, Horace, on mastication, 160. 

Flexner, investigator, 411. 

Flies, 283, 284, 285, 307. 

Floral envelope, 31. 

Flowers, 31, 32 ; 

imperfect, 39; 

pollination of, 35, 36, 37, 38, 39 ; 

relation to insects, 31, 33, 34-39. 
Fly, 283, 284, 285, 307. 
Food, definition, 118. 
Food tube, 116, 147. 
Foods, absorption, 157, 158; 

accessories, 128; 

adulteration, 138, 139; 

animal, 348-353; 

bacteria in, 258, 343-345 ; 

canned, 343, 344 ; 

care of, 294-296, 299; 

cold storage, 343 ; 

composition, 125-128; 

cost, 131; 

fuel value of, 119; 

functions of, 84, 118; 

in plants, 53, 57, 79-84, 87-92 ; 

made by plants, 79-84 ; 

nutrients, 53, 119; 

organic and inorganic, 53 ; 

plant, 323-329 ; 

preservatives, 344; 

study of, 118-137; 

see also Diet, Starch, Protein, etc. 
Foraminifera, 355. 
Forestry, 319-321, 370. 
Forests, conservation, 319, 320, 369; 

enemies of, 317-319; 

fires, 317, 318; 

of the United States, 315 ; 

relation to water supply, 5, 313- 

values of, 5, 314, 316; 

waste, 317. 
Formaldehyde, 260. 
Fossils, 250. 
Fox, 354, 355. 
Frog, 109-111; 

adaptations, 109; 

an amphibian, 246 ; 

blood corpuscle, 163 ; 

H. NEW CIV. BIOL. — 29 



Frog, brain, 200 ; 

capillar}' circulation, 172 ; 

central nervous system, 200 ; 

digestive tract of, 147 ; 

metamorphosis, 230, 231 ; 

mouth of, 149, 150; 

sense organs, 110; 

tongue, 110. 
Fruit, development, 41, 226; 

dispersal, 39, 40, 41. 
Fruits, canned, 344; 

garden, 328; 

orchard, 329; 

value as food, 123, 124. 
Fungi, 235, 236, 334-337. 
Fur-bearing animals, conservation, 378. 
Furs, 354, 355. 

Gall bladder, 156. 
Gall insects, 357. 
Gametes, 223. 
Ganghon, 198. 
Ganoid, Ganoidei, 245, 246. 
Garbage, disposal of, 297, 306, 307. 
Gas, for lighting, 294. 
Gas gangrene, 266, 274. 
Gastric glands, 153. 
Gastric juice, 153, 154. 
Gastrula, 227. 
Gelatin, value as food, 121. 
Generations, alternation of, 228. 
Genus, in classification, 234. 
Geotropism, 16, 67. 
Geranium, "Lady Washington," pol- 
lination, 37. 
Germ cells, 381, 382, 383. 
Germ diseases, 261-286. 
German measles, 269. 
Gill rakers, 244, 348. 
Gills of a fish, 244. 
Glanders, 271. 

Glands, digestive, 147, 148, 149, 153, 
156, 157 ; 

ductless or endocrine, 166, 167 ; 

gastric, 153; 

intestinal, 157; 

lymph, 173, 174; 

salivary, 149. 
Glomerulus, 188. 
Glue, 355. 

Glycogen, 156, 168. 

Goat, 354. 

Goiter, 166. 

Grafting, propagation by, 221. 

Grape sugar, 59, 60. 

Grasshopper, 27; 

life history, 228, 229; 

mouth parts, 34. 
Gravity, influence on living things, 16. 
Green plants, 45 ; 

economic value, 84, 323-333 ; 

give off oxygen, 85-86 ; 

make food, 75-84 ; 

see also Plants. 
Ground squirrels, 287. 
Growth, method of, 15. 
Gullet, 150, 152. 
Gymnosperms, 237. 
Gypsy moth, 363. 

Habits, 201; 

drink, 214; 

food, 134, 136; 

health, 212-214; 

how formed, 209-211; 

importance of, 210-211; 

in relation to a vocation, 402 ; 

rules for forming, 211-212. 
Haemoglobin, 163, 178. 
Hsemolysins, 166. 
Harvey, WilHam, biologist, 406. 
Havana, yellow fever in, 282. 
Hay fever, 276. 
Hay infusion, 97. 
Headache powders, 144. 
Health, 253 ; 

and clothing, 187 ; 

and exercise, 186. 
Hearing, sense of, 203, 204. 
Heart, 169, 170 ; 

of a fish, 245. 
Heating, methods of, 294. 
Heliotropism, 16. 
Hemiptera, 27, 242. 
Hemp, 330. 
Hen's egg, 231, 232. 
Heredity, 380, 381 ; 

of man, 396-401 ; 

transmitted by chromosomes, 381" 
383, 396 ; 



Heredity, work of Gregor Mendel, 

386, 387, 388, 389. 
Hermit crab, symbiosis, 105. 
Herring, 352, 372. 
Hibernation, 17. 
Hilum, 52. 

Hodge, Professor, cited, 298. 
Home surroundings, 293-297. 
Homology, 237. 
Honey, 351. 
Honeybees, 26, 351. 
Hooke, Robert, biologist, 44. 
Hookworm, 289, 290. 
Hormones, 148, 166, 167, 168. 
Hornaday, Dr., on birds, 375, 377. 
Home, Professor, rules for habits, 211. 
Horses, 391. 

Host, of a parasite, 31, 287. 
House fly, 283-285. 
Human machine, 112; see Body. 
Human race, 251; 

improvement of, 394. 
Humidity of air, 184. 
Humming birds, polhnation by, 38, 39. 
Humus, 10, 64. 

Hundred-calorie portions, 135. 
Huxley, Thomas Henry, biologist, 

405, 412. 
Hybridizing, 386-389. 
Hybrids, 386-389. 
Hydra, 108, 109, 111; 

symbiosis, 105. 
Hydrochloric acid, in digestion, 153, 

Hydrogen, in water, 8, 9. 
Hydrophobia, 274. 
Hydrotropism, 16. 
Hygiene, 1,22; 

of breathing, 181, 184 ; 

of mouth, 151 ; 

of muscles and bones, 114, 115; 

of skin, 112-113; 

pubhc, 308 ; 

school and infant, 310, 311. 
Hymenoptera, 26, 242. 
Hypocotyl, 52. 

Ice, use in home, 296. 

Ice cream, bacteria in, 298. 

Ichneumon fly, 358. 

Iguana, 352. 

Imago, 230. 

Imbibition, of root hairs, 71. 

Immunity, 270; 

acquired, 271 ; 

active, 272, 274-276; 

passive, 272, 273. 
Imperfect flowers, 39. 
Incinerator, 307. 
Incubation period, 269, 270. 
Infantile paralysis, 269. 
Infection, of wounds, 113. 
Infectious disease, 254, 261-286. 
Influenza, 264, 268, 295. 
Infusoria, 239. 

Inheritable characters, 397, 401. 
Inoculation, 274, 275. 
Inorganic soil, 64. 
Insecta, 242. 
Insectivora, 249. 
Insects, 25; 

classification, 242; 

eaten by birds, 359; 

enemies of forest, 319; 

eyes, 26, 33 ; 

feed on plants, 30 ; 

harmful, 295, 362-365; 

instincts, 209; 

relation to flowers, 31, 33, 34-39; 

sense of smell, 34 ; 

sense organs, 196 ; 

useful, 357; 

see also names of insects. 
Inspection, of factories, etc., 298-299 ; 

of food suppHes, 299-301. 
Instincts, 208. 
Insulin, 168. 
Intestinal fluid, 157. 
Intestine, 157, 158, 159; 

large, 159. 
Invertebrates, 243. 
Iodine, 260. 
Iris, 205. 
Irrigation, 313. 

Irritability, of protoplasm, 192. 
Ivory, 355. 

James, William, quoted, 211. 
Jenner, Edward, 271, 274. 
life, 407, 408. 



Jimson weed, 332. 
Juke family, 398. ' 
Jungle, 17,*^ 18. 
Jute, 331. 

Kallikak family, 398. 
Kdneys, 187, 188. 
Koch, Robert, life, 410. 
Kohl-rabi, 324. 

Labor, di\dsion of, 108-109. 

Laboratory equipment, 430. 

Lac insect, 357. 

Lacertilia, 247. 

Lactase, 157. 

Lacteals, 158, 174. 

Lactic acid, 340. 

Lactometer, 139. 

Ladybird, 28. 

Laitinen, Professor, cited, 141. 

Langerhans, Islands of, 167. 

Lantz, David E., quoted, 365. 

Larva, 27, 229. 

Larynx, 150. 

Lazear, Dr. Jesse, work on yellow 

fever, 280. 
Leather, 355. 
Leaves, 75-86; 

arrangement, 80; 

change of color, 81 ; 

changes in position, 194; 

dandelion, 80; 

evaporation from, 75 ; 

food, for man, 323 ; 

mosaic, 80; 

regulation of temperature, 79 ; 

respiration by, 85 ; 

starch made by, 81-84 ; 

structure, 47, 76, 77 ; 

transpiration, 77-79. 
Leeuwenhoek, Anton van, 44, 406. 
Legs of a bee, 33. 

Legumes, add to soil fertility, 341, 

value as food, 129. 
Lenticels, 86, 88. 
Leopard frog, 230, 231. 
Lepidoptera, 26, 27, 242. 
Lettuce, 324. 
Leucocytes, 168. 

Life, 14, 15; 

comes from life, 406. 
Life cycle, 228. 
Life history, 94, 228; 

of butterfly, 28 ; 

of house fly, 284 ; 

of mosquito, 280. 
Ligaments, 114. 
Light, influence on living things, 16 ; 

on bacteria, 258; 

on plants, 16, 80, 81. 
Lighting, methods of, 294. 
Limewater test, 11. 
Linen, 331. 
Lipase, 155. 

Lister, Sir Joseph, life, 410. 
Liver, 156, 168; 

blood supply, 172. 
Liver fluke, 228. 
Liverworts, 236. 
Lizard, 246. 
Lobster, 349, 350; 

conservation, 371. 
Lockjaw^, 273. 
Loeb, Jacques, cited, 14. 
Loosestrife, pollination, 37. 
Louse, 283. 

Lubbock, Sir John, biologist, 33. 
Lumbering, 317, 370. 
Lunches, school, 298. 
Lungs, 178, 179. 
Lymph, 168, 174. 
Lymph vessels, 173. 
Lysins, 165, 166, 276. 
Lysol, 260. 

Macronucleus, of Paramecium, 98. 

Malaria, 278-281. 

Malarial mosquito, 279, 280. 

Malarial parasite, 279. 

Malta fever, 266. 

Maltase, 157. 

Mammalia, 243. 

Mammals, 248, 249 ; 

adaptations, 237, 249; 

brain, 200; 

classified, 249; 

food for man, 353 ; 

reproduction, 232. 
Mammary glands, 249. 



Man, civilization, 250, 394; 

heredity, 396-401 ; 

in his environment, 21-22 ; 

need of conservation, 369 ; 

place in classification, 250 ; 

races, 251 ; 

see aho Blood, Diet, etc. 
Maple sugar, 324. 

Marriage, in relation to heredity, 401. 
Mastication, of food, 152. 
Mead, Professor A. D., experiment 

with starfish, 361. 
Measles, 268, 269, 270. 
Measures, 429. 
Meats, inspection, 299; 

value as food, 124, 131, 132. 
Medulla, 200. 
Medullarv ravs, 88. 
Melons, 325, 328. 
Membrane, mucous, 150; 

semi-permeable, 71, 72. 
Memory, 201. 
Mendel, Gregor, life, 413; 

work on heredity, 386-389. 
Mercurochrome, 260. 
Mesentery, 147. 
Mesoderm, 227. 
Metabolism, basal, 132-133. 
Metamorphosis, 30, 228; 

complete, 30, 229-230 ; 

incomplete, 229 ; 

of butterflv. 29-30; 

of frog, 230 ; 

of house flv, 284. 
Metchnikoff,"'Elias, 163-164, 411. 
Micrococci, 266. 

Micronucleus, of Paramecium, 98. 
Micropyle, 225. 
Microscope, 44. 
Midrib, 76. 
Mildews, 337. 
Milk, 249 ; 

adulteration, 139; 

care, 300-303 ; 

composition, 119, 128; 

disease germs in, 262, 264, 265, 
266, 301 ; 

fat globules in, 155; 

grades of, 302 ; 

kept with ice, 296 ; 

Milk, soured, 340; 

supply of, 258-259 ; 

value as food, 121, 123, 129, 132. 
Milking machines, 4. 
]\Iilkweed butterfly, 28, 29. 
Minerals, needed by plants, 65, 66 ; 

needed in food, 121. 
Mitosis, 48. 
JMolds, damage by, 336 ; 

flavor cheese, 336; 

groT\i;h of, 336 ; 

how to prevent, 336 ; 

reproduction, 222. 
MoUusca, classified, 242, 243. 
MoUusks, food for man, 348. 
^lolting, 229. 
ISlonarch butterfly, 28, 29. 
jNIonotremes, 249. 
Morgan, Thomas Hunt, biologist, 

393, 413. 
Mosquito, hfe history, 280 ; 

malarial, 279-281 ; 

yeUow fever, 281, 282. 
Mosses, 236. 
Mother of pearl. 356. 
Moths, 26, 27. 
Motor nerves, 199. 
jSlountain laurel, pollination, 37. 
Mouth, 149, 150. 
Mouth parts, of insects, 34. 
Mucous membrane, 150. 
Mumps, 269. 

Muscles, human, 114, 115. 
Musk, 355. 
Mutants, 385. 
Mycelium, 222. 
Myriapoda, 242. 

Narcotic, defined, 142. 
Natural selection theory, 383. 
Nectar, 31, 35. 
Nemathelminthes, 240. 
Nerve cell, 198 ; 

fatigue, 212. 
Nerves, 198, 199. 
Nervous system, 116, 197-202; 

functions of the parts, 201 ; 

health habits, 202, 213. 
Neuritis, caused by bad teeth, 151. 
Neurons, 198. 



Neuroptera, 242. 

Nicotine, 142. 

Nictitating membrane, 110. 

Nitrates, supplied to soil, 340, 341, 

Nitrogen, 8; 

cycle, 104, 105; 

fixed by bacteria, 341 ; 

in food", 120 ; 

needed b}^ plants, 65. 
Noguchi, Dr., investigator, 282, 411. 
Nos3, diseases of, 181-182. 
Nucleus of a cell, 45, 46. 
Nutrients, 53, 119; 

fuel values, 119; 

in common foods, 124 ; 

summary, 61. 
Nutritive ratio, 130. 
Nuts, 325, 329 ; 

value as food, 121, 124. 

Oat smut, 337. 
Oats, 328. 
Odonata, 242. 
Oils, 53, 119; 

animal, 355; 

test for, 54 ; 

vegetable, 331. 
Olfactorv nerve, 203. 
Olive, 331. 
Ommatidia, 33. 
Onions, 324, 325; 

cells of epidermis, 45. 
Operculum, 244. 
Ophidia, 247. 
Opium, 143, 144. 
Opsonins, 164, 276. 
Optic nerve, 205, 206. 
Orbit of eye, 205. 
Orchards, 329. 
Orchids, 36. 

Order, in classification, 235. 
Organ, 14, 47 ; 

see Leaves, Ears, Excretion, etc. 
Organic nutrients, 53 ; see Nutrients. 
Organic soil, 314. 
Organism, 14. 
Orthoptera, 27, 242. 
Osmosis, 71, 72, 73. 
Osmotic pressure, 72. 

Ovaries, 167. 

Ovary, in plant, 32, 226. 

Ovule, fertilization, 225. 

Owls, 360. 

Oxidation, 9; 

in germinating seeds, 57, 58 ; 

in the human body, 57, 168, 177. 
Oxygen, 9; 

cycle, 103; 

given off by plants, 82, 85 ; 

in air and water, 8 ; 

in respiration, 179; 

oxidation, 9. 
Oxyhsemoglobin, 163, 178. 
Oysters, 242, 348, 349; 

conservation, 371 ; 

enemies of, 361 ; 

pearl, 356. 

Pain, sense of, 202. 
Palate, hard and soft, 150, 
Palisade laver, 81 ; 

of leaf, 77. 
Pancreas, 154, 155, 167, 168. 
Paper, 316. 

Papilli) of tongue, 202. 
Paramecium, 08, 99; 

compared with amoeba, 108 ; 

receives stimuli, 193 ; 

responses, 195, 196. 
Parasites, 3 ; 

destruction of food by, 361 ; 

fungi, 335, 337; 

human, 399; 

protozoa, 278, 281-283 ; 

worms, 287-290. 
Parathyroid gland, 166. 
Paratyphoid, 276. 
Park, Dr. William H., cited, 262. 
Parotid gland, 149. 
Parsnip, 325. 
Passenger pigeon, 375. 
Pasteur, Louis, life, 408, 409, 410; 

pasteurization, 259; 

quoted, 3; 

work on rabies, 275 ; 

work on vaccination, 274. 
Pasteurization, 259, 302. 
Patent medicines, 143, 144. 
Pathogenic bacteria, 260. 



Pea, reproduction, 226. 

Pear, 325. 

Pearl-button industry, 356, 357. 

Pearls, 356. 

Peas, value as food, 124. 

Pellicle, of Paramecium, 98. 

Pepsin, 153, 154. 

Peptones, 154, 157. 

Perfumes, animal, 355. 

Pericardium, 169. 

Peristaltic movements, 153. 

Perspiration, 189, 190. 

Petals, 31, 32. 

Petiole, defined, 76. 

Petri dishes, 254. 

Phagocytes, 164, 165. 

Pharynx, 147, 150. 

Phenolphthalein, 70. 

Phloem, 90. 

Photosynthesis, 83. 

Phototropism, 16, 79-80. 

Phylloxera, 363. 

Phylum, in classification, 235. 

Physicist's view of the environment, 8. 

Physiological division of labor, 108- 

Physiology, 1. 
Pigeon, experiment with Vitamin B, 

Pimples, 113. 
Pinworms, 288. 
Pisces, 243. 
Pistil, 32. 
Pitcher plant, 92. 
Pith, 87, 88, 89. 
Pith rays, 88, 89. 
Pituitary gland, 167. 
Placenta, 232. 

Plague, 266, 271, 276. 285, 286, 287. 
Plankton, 348, 370. 
Plant breeding, 384-391. 
Plant cell, typical, 46, 49. 
Plants, 49, 51-106; 

classification, 234-237 ; 

diversity of form, 43 ; 

drug-producing, 331, 332; 

effect of light, 79-80; 

exert energy, 84; 

fibers, 329-331 ; 

give off oxygen in sunhght, 82, 85 ; 

Plants, harmful, 331-333; 

in relation to animals, 4, 30-31, 35, 
40, 102-106; 

influence of environment, 14-21 ; 

need mineral matter, 65, 66 ; 

oil from, 331; 

primary needs of, 107; 

reproduction, 219-226; 

respiration, 86; 

responses in, 192-196 ; 

seed dispersal, 39-41 ; 

simplest, 95; 

special digestive organs, 92 ; 

summary of the functions, 92-94; 

uses to man, 2-3, 5, 85, 323-333 ; 

without chlorophyll, 334-343 ; 

see also Bacteria and Fungi. 
Plasma, 162, 164, 165, 168. 
Plasmodium, 279. 
Platyhelminthes, 240. 
Pleura, 180. 

Pleurococcus, 96, 97, 219, 220. 
Plumule, defined, 52. 
Pneumonia, 264. 
Pocket garden, 67. 
Poison ivy, 331. 
Poisons, 271, 272 ; 

alcohol, 140; 

plant, 331, 333. 
Pollen, 32 ; 

grains, 224; 

growth, 224, 225, 226. 
Pollination, 35, 36, 37, 38, 39; 

artificial, 386. 

cross and self, 35. 
Pond scum, 223. 
Pons, 200. 

Porifera, classified, 239. 
Porkworm, 288. 
Portal circulation, 172. 
Posture, 114, 115. 
Potato beetle, 361. 
Potatoes, 324, 325; 

starch in, 129 ; 

value as food, 120, 123. 
Precipitins, 165, 276. 
Preservatives, of food, 344, 345. 
Pressure, sense of, 202. 
Pressure cooker, 344. 
Primates, 249, 250. 



Primrose, mutations, 385; 

pollination, 37. 
Proboscis, of insects, 27. 
Proglottids, 288. 
Prolegs, of caterpillar, 29. 
Pronuba, moth, 38. 
Propagation, vegetative, 220. 
Proteins, 53, 119; 

amount needed daily, 132 ; 

digested and stored in plants, 92 ; 

digestion of, in man, 153, 154, 155 

foods containing, 124; 

fuel value, 120 ; 

made by green plants, 84 ; 

not all good tissue builders, 120 ; 

poisonous, 272; 

spHt, 261, 271, 272; 

test for, 54, 55 ; 

value as food, 120, 130. 
Protoplasm, 44; 

composition, 120; 

discovery, 405; 

streaming of, 46. 
Protozoa, classified, 238, 239 ; 

food supply, 347 ; 

in rock building, 355 ; 

parasites, 278, 281, 282, 283 
Pseudopodia, of amoeba, 99. 
Pteridophytes, 236. 
Ptomaines, 272. 
Ptyalin, 151. 

Pidmonary circulation, 170. 
Pulse, 173. 
Pulvini, 194, 195. 
Pupa, 229 ; 

butterfly, 29. 
Pupil of eye, 205. 
Pure culture, 255, 256. 
Pure Food Law, 138. 
Pus, 113. 

Push cart T^dth glass covers, 300. 
Pyloric cseca, 245. 
Pylorus, 153. 

Quahog, 349. 
Quarantine, 268, 269. 
Quetlet's curve, 384, 385. 
Quinine, 279, 330. 

Rabies, 274, 282. 
Races of man, 251. 

Rats, 286, 287, 365. 

Reasoning, 202. 

Receptacle, 31, 32. 

Recessive characters, 388, 389, 397. 

Red blood corpuscle, 163. 

Redi, biologist, 406. 

Reed, Dr. Walter, investigator, 281, 

Reflex simple, 196, 197, 199 ; 

in instincts, 209. 
Refuse, in foods, 124. 
Regeneration, in animals, 221. 
Rennin, 153. 

Reproduction, by cell division, 219, 

in animals, 220, 222, 226-232 ; 

in plants, 219-226; 

in plants and animals, compared, 

indication of life, 152. 

of paraoecium, 99 ; 
Reproductive glands, 167. 
Reptiles, 246, 247; 

food of man, 35. 
ReptiHa, 243. 
Respiration, 177-183; 

artificial, 182, 183; 

cell, 179, 180; 

effect of exercise, 186 ; 

mechanics of, 180-183; 

necessity for, 177; 

of plants, 86 ; 

organs of. 111, 177, 178. 
Response to stimuli, an indication of 
life, 14-15; 

in plants and animals, 192-195. 
Retina, 205. 
Rheumatism, 151, 182. 
Rhizoids, 222. 
Rhizopoda, 239. 
Rice, 328. 

Rickets, deficiency disease, 123. 
Rind of corn stem, 90. 
Ringworm, 336. 
Robins, food of, 359. 
Rockefeller Foundation, work on 

hookworm, 290. 
Rodentia, 249. 

Roosevelt, Theodore, quoted, 310. 
Roosters, heads of, 381. 



Root hairs, 68, 69, 70, 72. 

Root pressure, 91. 
Roots, 66-73 ; 

downward growth of, 66-67; 

food for man, 325 ; 

give out acid, 70 ; 

growth toward water, 67 ; 

primary, secondary, and tertiary, 

root hairs, 68, 69, 70, 72 ; 

structure of, 67, 68, 69. 
Ross, Major, investigator, 411. 
Rotation of crops, 341, 342. 
Roughage, in foods, 124. 
Roundworms, 240, 288, 289. 
Roux, investigator, 409. 
Russian thistle, 333. 
Rusts, 337. 
Rye, 328. 

SaHva, action of, 149. 
Sahvary glands, 149. 
Salmon, 352, 373, 374. 
Salt, a food, 121 ; 

a food preservative, 344. 
Sanitarium for tuberculosis, 309. 
Sanitation, 22. 
Saprophytes, 334. 
Scallops, 349, 371. 
Scarlet fever, 266, 268, 269; 

Dick test, 273. 
Scavengers, 357, 360. 
Schaefer method, of artificial respira- 
tion, 182, 183. 
Schick test, 273. 
Schleiden, biologist, 405. 
School, surroundings, 297. 
School and infant hj^giene, work of 

health board, 310, 311. 
Schwann, biologist, 406. 
Scurvy, dexiciency disease, 123. 
Sea anemone, 240 ; 

symbiosis, 105. 
Sea cucumber, 241. 
Sea lily, 241. 
Sea Hon, 249. 
Sea urchin, 241. 
Seals 354. 

Secretin, normone. 155, 166. 
Secretion, 148, 166. 

Seeds, development, 226, 361 ; 

dispersal, 39, 40, 41 ; 

food of man, 325-328. 
Seeing, 205-206. 
Segmented worms, 241. 
Segments, of insect, 25. 
Segregation, law of, 388. 
Selection, natural and artificial, 383, 

Selective planting, 385. 
Self-pollination, 35, 36. 
Semicircular canals, 204. 
Semi-permeable membrane, 71, 72. 
Sense organs, 196, 197, 202-206 ; 

health habits, 213 ; 

of frog, 110. 
Sensory hair, 196, 197. 
Sensory nerves, 198. 
Sepal, 31, 32. 

Septic sore throat, 266, 269. 
Septic tank, 297. 

Serum, antitoxin, 272, 273, 274, 276. 
Sewage disposal, 304, 305, 306 ; 

pollution of water supply, 303-305. 
Sexual reproduction, 222, 223 ; 

in animals, 227-232 ; 

in plants, 223-226. 
Shad, 373. 
Sheep, 353, 354; 

fiver fluke, 228. 
Shelf fungus, 335. 
SheUac, 357. 
Shoulders, round, 114. 
Shrimps, 350; 

ears, 197. 
Sieve tubes, 87, 89, 90, 91. 
Silk industry, 353, 354. 
Silkworm, 27, 353, 354. 
Simplest organisms, 95. 
Siphonaptera, 242. 
Sirenia, 249. 
Skeleton of man, 114 ; 

of vertebrates (dog), 243. 
Skin, 112, 113; 

as an organ of excretion, 189 ; 

frog's, 110; 

infections, 113; 

regulates body heat, 190. 
Sleep, necessity of, 212. 
Sleeping places, outdoor, 185. 



Sleeping rooms, ventilation of, 184- 

Sleeping sickness, 283. 
Sludge, disposal of, 305. 
Smallpox, 269, 282 ; 

vaccination, 271, 274, 407, 408. 
Smell, sense of, 203. 
Smuts, 337. 
Snail, 242. 
Snakes, 246; 

destructive, 366; 

useful, 358; 

venoms, 272, 274. 
Social inheritance, 395. 
Society, lessons of biology, 6. 
Soil, capacity for holding water, 65 ; 

composition of, 10, 63-65 ; 

erosion of, 314; 

fertihzing, 341-343 ; 

inorganic and organic, 64. 
Soil water, 65. 
Solar engines, 79. 
Solutes, 9. 
Solution, 9. 

Sound, character of, 205. 
Sparrow, 360. 

Spawning, of fishes, 372-373. 
Species, 234 ; 

new, 383, 385. 
Specific disease, 260. 
Sperm 223, 224, 226, 227. 
Sperm cell, 226, 227; 

development, 381, 382, 383. 
Spermatophytes, 237. 
Spices, adulteration, 139. 
Spider, 28, 241. 
Spinal cord, 199, 100. 
Spine, curvature of, 115. 
Spiracles, of insect, 26. 
Spirillum, 96, 256. 
Spirochsetes, 282. 
Spirogyra, 223. 
Spleen, 156. 

Split proteins, 261, 271, 272. 
.Sponges, 239, 355. 
Spongy tissue, of leaf, 772. 
Sporangia, 222. 
Spores, asexual, 222, 223, 228 ; 

sexual, 223. 
Sporozoa, 239. 

Sports, 385. 
Sprengel, Conrad, 35. 
Squid, 242. 
Stamen, 32. 
Staphjdococci, 266. 
Starch, 53 ; 

changed to grape sugar, 59, 60 ; 

digested in plants, 91 ; 

digestion by man, 149, 154, 155 ; 

fuel value, 119-120; 

grains, 60, 129 ; 

made bv green leaves, 81-84; 

test for^ 53, 54. 
Starch making, 81, 82, 84. 
Starfish, 241 ; 

food of, 361; 

regeneration, 220. 
Statocysts, 197. 
Stems, dicotyledonous, 87, 88, 90; 

food of man, 324 ; 

monocot^dedonous, 89, 90, 91; 

passage of fluids, 75, 91 ; 

passage of food, 89 ; 

rise of water in, 91 ; 

structure of, 87-91. 
Sterihzation, 2-54, 256, 258. 
Sterilizer, 254. 
Stigma, 32. 
Stiles, Dr. C. W., work on hookwoim, 

Stillman, Dr. E. G., cited, 142. 
Stimulants, 139. 
StimuK, 15; 

of plants and aniiTxals, 192, 193, 
Sting, 26. 
Stipules, 76. 

Stockard, Dr., cffced, 141. 
Stomach, 153, 154. 
Stomata, 76, r7. 
Streaming of protoplasm, 46. 
Street cleaning, 306, 307. 
Streptococci, 113. 
Sturgeon, 374. 
Style, 32. 

Sublingual gland, 149. 
Submaxillary gland, 149. 
Substance, defined, 8. 
Succus entericus, 157. 
Sucrase, 157. 



Suffocation, 182. 
Sugar, 53, 60; 

absorption, 158; 

digestion, 157; 

food preservative, 344 ; 

fuel value, 119-120; 

test for, 59. 
Sugar cane, 324. 
Summer complaint, 285. 
Sun a source of energy, 79. 
Sundew, 92. 
Sunlight, necessarv for starch making, 

Suprarenals, 167. 
Sweat gland, 189. 
Swim bladder of fish, 245. 
Symbiosis, 105. 
Synapse, 198. 
SyphiHs, 282, 410. 
Systemic circulation, 170. 

Tactile corpuscles, 202. 
Tadpole, 230, 231. 
Tapeworm, 240, 287, 288. 
Taste, sense of, 202, 203. 
Tea, stimulant, 139. 
Teeth, 150, 151 ; 

care of, 151-152, 311. 
Teleost, Teleostei, 245, 246. 
Temperature, influence on living 
things, 17; 

of the body, 189; 

sense of, 202. 
Terrapin, 352. 
Testes, 167. 
Tests, for carbon dioxide, 11; 

for nutrients, 54, 55, 59. 
Tetanus, 266, 273, 274. 
Thallophytes, 235. 
Thermotropism, 17. 
Thinking, 201. 
Thoracic duct, 158, 174. 
Thorax, of insect, 25. 
Throat, diseases of, 181-182. 
Thrombin, 165. 
Thymus gland, 167. 
Thyroid gland, 166. 
Tick fever, 283. 
Tissue, 47. 
Tissue building, 120. 

Toad, 358. 

Tobacco, effects of, 142. 

Tobacco crop, 332. 

Tomatoes, value as food, 123. 

Tongue, 150. 

Tonsils, enlarged, 182, 310. 

Touch, sense of, 202. 

Tourniquet, 175. 

Toxin-antitoxin treatment, 273. 

Toxins, 260, 261, 271, 272. 

Trachea, 150. 

Tradescantia leaves, 81. 

Transfusion of blood, 166. 

Transpiration, 77-79. 

Trees, 313-321; 

injured by insects, 363, 364; 

see Forests. 
Trial and error method, 195, 196. ' 
Triangle of life, 395. 
Trichina, 240, 288. 
Trichinosis, 288. 
Trillium, 237. 
Tropics, jungle, 17, 18. 
Tropisms, 15-17, 192-195; 

value, 17. 
Trout, development of, 372. 
Trypanosomes, 283. 
Trj^psin, 155. 
Tsetse fly, 283. 
Tuberculosis, 262, 263, 270, 285 ; 

carried by milk, 301 ; 

fought by health boards, 309 ; 

recurrence in same houses, 293, 294. 
Turnip, 325. 
Turtle, 246, 352. 
Tussock moth, 364, 
Tympanic membrane, 204. 
Tyndall, Professor, biologist, 406. 
Typhoid fever, 264, 285; 

carried by milk, 301 ; 

carried by water supply, 303-305 ; 

vaccination against, 275 ; 

Widal test, 165, 275. 
Typhus fever, 283. 

Ungulata, 249. 
Unit characters, 388. 
Urine, excretion, 188. 
Urodela, 246. 
Uterus, 232. 



Vaccination, 274, 275, 407. 
Vaccines, 276; 

work of Pasteur, 409. 
Vacuoles, 45, 46. 
Valves, in heart, 170; 

in veins, 173. 
Variation, 381 ; 

continuous and discontinuous, 385; 

Darwin's theory, 383, 384. 
Vaucheria, reproduction, 223, 224. 
Vegetables, canned, 343, 344; 

garden, 328; 

value as food, 123, 130, 132. 
Vegetative propagation, 220, 221. 
Veins, 169, 172, 173. 
Venae cavse, 172. 
Ventilation, 183, 184, 185. 
Ventricle, 169, 170. 
Venus's flytrap, 92. 
Vermiform appendix, 159. 
Vertebral column, 243. 
Vertebrata, classified, 243-250. 
Vertebrates, classified, 243-250. 
Vesture, of insect, 25. 
VilH, 157, 158. 
Vinegar, 340. 
Virginia creeper, 331. 
Vitamins, 119, 121-123, 124; 

table of, 122. 
Vocation, choice of, 402-403. 
Voit, cited, 132. 
Voluntary acts, 202. 
Von Behring, work on antitoxin, 272. 
Vorticella, 238. 
Vries, Hugo de, 385, 413. 

Wallace, Alfred Russel, biologist, 412. 
Wastes, disposal of, 296-297. 
Water, composition, 8, 9; 
food of man, 121, 124; 

Water, influence on living things, 16 ; 

source of disease infection, 264, 265, 

supply, 296, 303, 304. 
Weeds, characteristics, 13, 14, 332- 

checked by animals, 357, 360, 361 ; 

harm done bv, 332-333. 
Weevils, 28, 363, 364. 
Weissman, August, biologist, 412, 
Whale, 348, 355. 
Wheat, 325, 327, 328 ; 

bearded and beardless, 385 ; 

value as food, 121. 
Wheat rust, 337. 
Whooping cough, 264, 269. 
Widal test, 165, 275. 
Wind, pollination by, 39. 
Windpipe, 150, 178. 
Winslow, Dr. C. E. A., quoted, 308. 
Wood, 87, 88; 

uses of, 316, 317, 369. 
Woolen industry, 354. 
Worms, 240, 241 ; 

parasites, 287-290. 
Wrens, 376. 

Xeropthalmia, 123. 
Xylem, 91. 

Yeast, 338, 339; 

reproduction, 222, 223. 

value as food, 123. 
Yeast cakes, 338. 
Yellow fever, 281, 282. 
Yucca, polhnation, 37-38. 

Zygospores, 223. 
Zygotes, 223. 
Zymases, 338. 

University of